Sensim Math · Depth 한국어

← 2-2 · Reach the next hour, then add the rest · Elapsed Time and Base-Sixty Regrouping

Reach the next hour, then add the rest · 12 practice problems

2.MD.C.73.MD.A.1

Generated variants — 12

Freshly produced from the archetype’s parameters — problem, figure, and solution derived together.

Variant 1 answer: 5:04 p.m.

Mia started reading at 3:553{:}55 p.m. She read a storybook for 3939 minutes, and then read a science book for 3030 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 3:55 p.m. She read a storybook for 39 minutes, then a science book for 30 minutes. Find the time she finished.

Givens
  • Start time is 3:55 p.m.
  • First reading lasts 39 minutes.
  • Second reading lasts 30 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 39 and 30 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 3:55 it takes 5 minutes to reach 4:00.
60−55=5 minutes⇒3:55+5=4:0060 - 55 = 5 \text{ minutes} \Rightarrow 3{:}55 + 5 = 4{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 39 minutes; 5 of those reached 4:00, so 34 minutes remain.
39−5=34⇒4:00+34=4:3439 - 5 = 34 \Rightarrow 4{:}00 + 34 = 4{:}34
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 30 minutes to 4:34. First reach 5:00 (26 minutes), leaving 4 minutes, so finish at 5:04.
4:34+26=5:00,30−26=4⇒5:00+4=5:044{:}34 + 26 = 5{:}00,\quad 30 - 26 = 4 \Rightarrow 5{:}00 + 4 = 5{:}04
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 5:04 p.m.

Review

Total reading time is 39 + 30 = 69 minutes = 1 hour 9 minutes. Starting at 3:55, add 1 hour to get 4:55, then 9 minutes to get 5:04 p.m. -- matching the step-by-step result.

Add the two durations first: 39 + 30 = 69 minutes = 1 h 9 min, then add to 3:55 p.m. directly to land on 5:04 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 2 answer: 4:31 p.m.

Mia started reading at 2:552{:}55 p.m. She read a storybook for 4848 minutes, and then read a science book for 4848 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 2:55 p.m. She read a storybook for 48 minutes, then a science book for 48 minutes. Find the time she finished.

Givens
  • Start time is 2:55 p.m.
  • First reading lasts 48 minutes.
  • Second reading lasts 48 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 48 and 48 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 2:55 it takes 5 minutes to reach 3:00.
60−55=5 minutes⇒2:55+5=3:0060 - 55 = 5 \text{ minutes} \Rightarrow 2{:}55 + 5 = 3{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 48 minutes; 5 of those reached 3:00, so 43 minutes remain.
48−5=43⇒3:00+43=3:4348 - 5 = 43 \Rightarrow 3{:}00 + 43 = 3{:}43
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 48 minutes to 3:43. First reach 4:00 (17 minutes), leaving 31 minutes, so finish at 4:31.
3:43+17=4:00,48−17=31⇒4:00+31=4:313{:}43 + 17 = 4{:}00,\quad 48 - 17 = 31 \Rightarrow 4{:}00 + 31 = 4{:}31
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 4:31 p.m.

Review

Total reading time is 48 + 48 = 96 minutes = 1 hour 36 minutes. Starting at 2:55, add 1 hour to get 3:55, then 36 minutes to get 4:31 p.m. -- matching the step-by-step result.

Add the two durations first: 48 + 48 = 96 minutes = 1 h 36 min, then add to 2:55 p.m. directly to land on 4:31 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 3 answer: 3:22 p.m.

Mia started reading at 1:401{:}40 p.m. She read a storybook for 5151 minutes, and then read a science book for 5151 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 1:40 p.m. She read a storybook for 51 minutes, then a science book for 51 minutes. Find the time she finished.

Givens
  • Start time is 1:40 p.m.
  • First reading lasts 51 minutes.
  • Second reading lasts 51 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 51 and 51 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 1:40 it takes 20 minutes to reach 2:00.
60−40=20 minutes⇒1:40+20=2:0060 - 40 = 20 \text{ minutes} \Rightarrow 1{:}40 + 20 = 2{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 51 minutes; 20 of those reached 2:00, so 31 minutes remain.
51−20=31⇒2:00+31=2:3151 - 20 = 31 \Rightarrow 2{:}00 + 31 = 2{:}31
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 51 minutes to 2:31. First reach 3:00 (29 minutes), leaving 22 minutes, so finish at 3:22.
2:31+29=3:00,51−29=22⇒3:00+22=3:222{:}31 + 29 = 3{:}00,\quad 51 - 29 = 22 \Rightarrow 3{:}00 + 22 = 3{:}22
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 3:22 p.m.

Review

Total reading time is 51 + 51 = 102 minutes = 1 hour 42 minutes. Starting at 1:40, add 1 hour to get 2:40, then 42 minutes to get 3:22 p.m. -- matching the step-by-step result.

Add the two durations first: 51 + 51 = 102 minutes = 1 h 42 min, then add to 1:40 p.m. directly to land on 3:22 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 4 answer: 6:13 p.m.

Mia started reading at 4:554{:}55 p.m. She read a storybook for 3939 minutes, and then read a science book for 3939 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 4:55 p.m. She read a storybook for 39 minutes, then a science book for 39 minutes. Find the time she finished.

Givens
  • Start time is 4:55 p.m.
  • First reading lasts 39 minutes.
  • Second reading lasts 39 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 39 and 39 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 4:55 it takes 5 minutes to reach 5:00.
60−55=5 minutes⇒4:55+5=5:0060 - 55 = 5 \text{ minutes} \Rightarrow 4{:}55 + 5 = 5{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 39 minutes; 5 of those reached 5:00, so 34 minutes remain.
39−5=34⇒5:00+34=5:3439 - 5 = 34 \Rightarrow 5{:}00 + 34 = 5{:}34
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 39 minutes to 5:34. First reach 6:00 (26 minutes), leaving 13 minutes, so finish at 6:13.
5:34+26=6:00,39−26=13⇒6:00+13=6:135{:}34 + 26 = 6{:}00,\quad 39 - 26 = 13 \Rightarrow 6{:}00 + 13 = 6{:}13
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 6:13 p.m.

Review

Total reading time is 39 + 39 = 78 minutes = 1 hour 18 minutes. Starting at 4:55, add 1 hour to get 5:55, then 18 minutes to get 6:13 p.m. -- matching the step-by-step result.

Add the two durations first: 39 + 39 = 78 minutes = 1 h 18 min, then add to 4:55 p.m. directly to land on 6:13 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 5 answer: 3:01 p.m.

Mia started reading at 1:401{:}40 p.m. She read a storybook for 3030 minutes, and then read a science book for 5151 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 1:40 p.m. She read a storybook for 30 minutes, then a science book for 51 minutes. Find the time she finished.

Givens
  • Start time is 1:40 p.m.
  • First reading lasts 30 minutes.
  • Second reading lasts 51 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 30 and 51 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 1:40 it takes 20 minutes to reach 2:00.
60−40=20 minutes⇒1:40+20=2:0060 - 40 = 20 \text{ minutes} \Rightarrow 1{:}40 + 20 = 2{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 30 minutes; 20 of those reached 2:00, so 10 minutes remain.
30−20=10⇒2:00+10=2:1030 - 20 = 10 \Rightarrow 2{:}00 + 10 = 2{:}10
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 51 minutes to 2:10. First reach 3:00 (50 minutes), leaving 1 minutes, so finish at 3:01.
2:10+50=3:00,51−50=1⇒3:00+1=3:012{:}10 + 50 = 3{:}00,\quad 51 - 50 = 1 \Rightarrow 3{:}00 + 1 = 3{:}01
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 3:01 p.m.

Review

Total reading time is 30 + 51 = 81 minutes = 1 hour 21 minutes. Starting at 1:40, add 1 hour to get 2:40, then 21 minutes to get 3:01 p.m. -- matching the step-by-step result.

Add the two durations first: 30 + 51 = 81 minutes = 1 h 21 min, then add to 1:40 p.m. directly to land on 3:01 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 6 answer: 3:01 p.m.

Mia started reading at 1:551{:}55 p.m. She read a storybook for 3939 minutes, and then read a science book for 2727 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 1:55 p.m. She read a storybook for 39 minutes, then a science book for 27 minutes. Find the time she finished.

Givens
  • Start time is 1:55 p.m.
  • First reading lasts 39 minutes.
  • Second reading lasts 27 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 39 and 27 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 1:55 it takes 5 minutes to reach 2:00.
60−55=5 minutes⇒1:55+5=2:0060 - 55 = 5 \text{ minutes} \Rightarrow 1{:}55 + 5 = 2{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 39 minutes; 5 of those reached 2:00, so 34 minutes remain.
39−5=34⇒2:00+34=2:3439 - 5 = 34 \Rightarrow 2{:}00 + 34 = 2{:}34
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 27 minutes to 2:34. First reach 3:00 (26 minutes), leaving 1 minutes, so finish at 3:01.
2:34+26=3:00,27−26=1⇒3:00+1=3:012{:}34 + 26 = 3{:}00,\quad 27 - 26 = 1 \Rightarrow 3{:}00 + 1 = 3{:}01
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 3:01 p.m.

Review

Total reading time is 39 + 27 = 66 minutes = 1 hour 6 minutes. Starting at 1:55, add 1 hour to get 2:55, then 6 minutes to get 3:01 p.m. -- matching the step-by-step result.

Add the two durations first: 39 + 27 = 66 minutes = 1 h 6 min, then add to 1:55 p.m. directly to land on 3:01 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 7 answer: 8:02 p.m.

Mia started reading at 6:506{:}50 p.m. She read a storybook for 5454 minutes, and then read a science book for 1818 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 6:50 p.m. She read a storybook for 54 minutes, then a science book for 18 minutes. Find the time she finished.

Givens
  • Start time is 6:50 p.m.
  • First reading lasts 54 minutes.
  • Second reading lasts 18 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 54 and 18 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 6:50 it takes 10 minutes to reach 7:00.
60−50=10 minutes⇒6:50+10=7:0060 - 50 = 10 \text{ minutes} \Rightarrow 6{:}50 + 10 = 7{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 54 minutes; 10 of those reached 7:00, so 44 minutes remain.
54−10=44⇒7:00+44=7:4454 - 10 = 44 \Rightarrow 7{:}00 + 44 = 7{:}44
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 18 minutes to 7:44. First reach 8:00 (16 minutes), leaving 2 minutes, so finish at 8:02.
7:44+16=8:00,18−16=2⇒8:00+2=8:027{:}44 + 16 = 8{:}00,\quad 18 - 16 = 2 \Rightarrow 8{:}00 + 2 = 8{:}02
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 8:02 p.m.

Review

Total reading time is 54 + 18 = 72 minutes = 1 hour 12 minutes. Starting at 6:50, add 1 hour to get 7:50, then 12 minutes to get 8:02 p.m. -- matching the step-by-step result.

Add the two durations first: 54 + 18 = 72 minutes = 1 h 12 min, then add to 6:50 p.m. directly to land on 8:02 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 8 answer: 8:01 p.m.

Mia started reading at 6:406{:}40 p.m. She read a storybook for 4848 minutes, and then read a science book for 3333 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 6:40 p.m. She read a storybook for 48 minutes, then a science book for 33 minutes. Find the time she finished.

Givens
  • Start time is 6:40 p.m.
  • First reading lasts 48 minutes.
  • Second reading lasts 33 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 48 and 33 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 6:40 it takes 20 minutes to reach 7:00.
60−40=20 minutes⇒6:40+20=7:0060 - 40 = 20 \text{ minutes} \Rightarrow 6{:}40 + 20 = 7{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 48 minutes; 20 of those reached 7:00, so 28 minutes remain.
48−20=28⇒7:00+28=7:2848 - 20 = 28 \Rightarrow 7{:}00 + 28 = 7{:}28
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 33 minutes to 7:28. First reach 8:00 (32 minutes), leaving 1 minutes, so finish at 8:01.
7:28+32=8:00,33−32=1⇒8:00+1=8:017{:}28 + 32 = 8{:}00,\quad 33 - 32 = 1 \Rightarrow 8{:}00 + 1 = 8{:}01
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 8:01 p.m.

Review

Total reading time is 48 + 33 = 81 minutes = 1 hour 21 minutes. Starting at 6:40, add 1 hour to get 7:40, then 21 minutes to get 8:01 p.m. -- matching the step-by-step result.

Add the two durations first: 48 + 33 = 81 minutes = 1 h 21 min, then add to 6:40 p.m. directly to land on 8:01 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 9 answer: 4:28 p.m.

Mia started reading at 2:552{:}55 p.m. She read a storybook for 5454 minutes, and then read a science book for 3939 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 2:55 p.m. She read a storybook for 54 minutes, then a science book for 39 minutes. Find the time she finished.

Givens
  • Start time is 2:55 p.m.
  • First reading lasts 54 minutes.
  • Second reading lasts 39 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 54 and 39 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 2:55 it takes 5 minutes to reach 3:00.
60−55=5 minutes⇒2:55+5=3:0060 - 55 = 5 \text{ minutes} \Rightarrow 2{:}55 + 5 = 3{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 54 minutes; 5 of those reached 3:00, so 49 minutes remain.
54−5=49⇒3:00+49=3:4954 - 5 = 49 \Rightarrow 3{:}00 + 49 = 3{:}49
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 39 minutes to 3:49. First reach 4:00 (11 minutes), leaving 28 minutes, so finish at 4:28.
3:49+11=4:00,39−11=28⇒4:00+28=4:283{:}49 + 11 = 4{:}00,\quad 39 - 11 = 28 \Rightarrow 4{:}00 + 28 = 4{:}28
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 4:28 p.m.

Review

Total reading time is 54 + 39 = 93 minutes = 1 hour 33 minutes. Starting at 2:55, add 1 hour to get 3:55, then 33 minutes to get 4:28 p.m. -- matching the step-by-step result.

Add the two durations first: 54 + 39 = 93 minutes = 1 h 33 min, then add to 2:55 p.m. directly to land on 4:28 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 10 answer: 8:03 p.m.

Mia started reading at 6:456{:}45 p.m. She read a storybook for 4242 minutes, and then read a science book for 3636 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 6:45 p.m. She read a storybook for 42 minutes, then a science book for 36 minutes. Find the time she finished.

Givens
  • Start time is 6:45 p.m.
  • First reading lasts 42 minutes.
  • Second reading lasts 36 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 42 and 36 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 6:45 it takes 15 minutes to reach 7:00.
60−45=15 minutes⇒6:45+15=7:0060 - 45 = 15 \text{ minutes} \Rightarrow 6{:}45 + 15 = 7{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 42 minutes; 15 of those reached 7:00, so 27 minutes remain.
42−15=27⇒7:00+27=7:2742 - 15 = 27 \Rightarrow 7{:}00 + 27 = 7{:}27
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 36 minutes to 7:27. First reach 8:00 (33 minutes), leaving 3 minutes, so finish at 8:03.
7:27+33=8:00,36−33=3⇒8:00+3=8:037{:}27 + 33 = 8{:}00,\quad 36 - 33 = 3 \Rightarrow 8{:}00 + 3 = 8{:}03
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 8:03 p.m.

Review

Total reading time is 42 + 36 = 78 minutes = 1 hour 18 minutes. Starting at 6:45, add 1 hour to get 7:45, then 18 minutes to get 8:03 p.m. -- matching the step-by-step result.

Add the two durations first: 42 + 36 = 78 minutes = 1 h 18 min, then add to 6:45 p.m. directly to land on 8:03 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 11 answer: 3:12 p.m.

Mia started reading at 1:501{:}50 p.m. She read a storybook for 3535 minutes, and then read a science book for 4747 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 1:50 p.m. She read a storybook for 35 minutes, then a science book for 47 minutes. Find the time she finished.

Givens
  • Start time is 1:50 p.m.
  • First reading lasts 35 minutes.
  • Second reading lasts 47 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 35 and 47 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 1:50 it takes 10 minutes to reach 2:00.
60−50=10 minutes⇒1:50+10=2:0060 - 50 = 10 \text{ minutes} \Rightarrow 1{:}50 + 10 = 2{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 35 minutes; 10 of those reached 2:00, so 25 minutes remain.
35−10=25⇒2:00+25=2:2535 - 10 = 25 \Rightarrow 2{:}00 + 25 = 2{:}25
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 47 minutes to 2:25. First reach 3:00 (35 minutes), leaving 12 minutes, so finish at 3:12.
2:25+35=3:00,47−35=12⇒3:00+12=3:122{:}25 + 35 = 3{:}00,\quad 47 - 35 = 12 \Rightarrow 3{:}00 + 12 = 3{:}12
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 3:12 p.m.

Review

Total reading time is 35 + 47 = 82 minutes = 1 hour 22 minutes. Starting at 1:50, add 1 hour to get 2:50, then 22 minutes to get 3:12 p.m. -- matching the step-by-step result.

Add the two durations first: 35 + 47 = 82 minutes = 1 h 22 min, then add to 1:50 p.m. directly to land on 3:12 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!
Variant 12 answer: 8:04 p.m.

Mia started reading at 6:556{:}55 p.m. She read a storybook for 3333 minutes, and then read a science book for 3636 minutes.

At what time (p.m.) did Mia finish reading?

Show solution

Understand

Mia started reading at 6:55 p.m. She read a storybook for 33 minutes, then a science book for 36 minutes. Find the time she finished.

Givens
  • Start time is 6:55 p.m.
  • First reading lasts 33 minutes.
  • Second reading lasts 36 minutes.
Unknowns
  • The clock time (p.m.) when Mia finished reading.
Constraints
  • Time runs forward; 60 minutes makes one hour.

Plan

#7 Identify Subproblems · also uses: #11 Work Backwards

Rather than adding 33 and 36 across an awkward minute boundary, first add just enough minutes to reach the next whole hour, then add the rest. This 'make o'clock then add' approach keeps each addition simple.

Execute

#7 Identify Subproblems 2.MD.C.7
From 6:55 it takes 5 minutes to reach 7:00.
60−55=5 minutes⇒6:55+5=7:0060 - 55 = 5 \text{ minutes} \Rightarrow 6{:}55 + 5 = 7{:}00
Topping the minutes up to 60 lands exactly on the next whole hour, which is easy to add onto.
#7 Identify Subproblems 3.MD.A.1
The storybook reading was 33 minutes; 5 of those reached 7:00, so 28 minutes remain.
33−5=28⇒7:00+28=7:2833 - 5 = 28 \Rightarrow 7{:}00 + 28 = 7{:}28
After hitting the o'clock, adding the leftover minutes is a simple within-the-hour jump.
#7 Identify Subproblems 3.MD.A.1
Now add 36 minutes to 7:28. First reach 8:00 (32 minutes), leaving 4 minutes, so finish at 8:04.
7:28+32=8:00,36−32=4⇒8:00+4=8:047{:}28 + 32 = 8{:}00,\quad 36 - 32 = 4 \Rightarrow 8{:}00 + 4 = 8{:}04
Using the same make-o'clock trick again keeps the second addition simple.
Answer: 8:04 p.m.

Review

Total reading time is 33 + 36 = 69 minutes = 1 hour 9 minutes. Starting at 6:55, add 1 hour to get 7:55, then 9 minutes to get 8:04 p.m. -- matching the step-by-step result.

Add the two durations first: 33 + 36 = 69 minutes = 1 h 9 min, then add to 6:55 p.m. directly to land on 8:04 p.m.

Standards · min grade 3

  • 2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading and stepping the start time up to the next whole hour.
  • 3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Adding the reading durations across hour boundaries to find the finish time.
💡 Bump up to the next o'clock first, then add what's left: a Grade 3 time-adding shortcut!