Depth · one concept from first principles · step 2 of 4
Mia is 5 cm taller than Liam, so Liam is 5 cm shorter than Mia.
'Taller by 5' run backwards means the shorter person is the taller minus 5.
2.MD.B.5Work BackwardsBecause Mia is 5 cm taller than Liam, Liam's height is Mia's height minus 5 cm.
Saying Mia is 5 cm taller than Liam means her height is Liam's whole height with an extra 5 cm stacked on top, so Mia's height equals Liam's height plus 5 cm.
Once Liam's height plus 5 cm makes Mia's height, taking that same 5 cm back off Mia's height gives Liam's height again.
Change 1 m 25 cm into centimeters: 100 + 25 = 125 cm.
Same-unit lengths can be subtracted once both are in centimeters.
2.MD.B.5Draw A DiagramTake 5 cm off Mia's 125 cm: 125 - 5 = 120 cm, which is 1 m 20 cm.
120 cm regroups into 1 m (100 cm) and 20 cm left over.
2.MD.B.5Work BackwardsIf someone is taller by 5 cm, the other is just 5 cm less — simple Grade 2 take-away with lengths!
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The same shape shows up later on the AMC, as Arithmetic Expression Decomposition, Branching State Enumeration, Multiplicative Ratio with Integrality Constraints. Why the shapes repeat →