Problem
Add the boys and girls to find the total number of students who will receive notebooks.
Adding two 3-digit numbers is a basic place-value skill: ones, tens, hundreds line up and you carry as needed.
4.NBT.B.4Identify SubproblemsEach of the 841 students gets 2 notebooks, so multiply the number of students by 2 to get the total notebooks needed.
Two notebooks per student is the same number added 841 times — multiplying by 2 is just doubling, an easy multi-digit multiplication.
4.NBT.B.5Analyze The UnitsPacks come in tens and 1680 would leave 2 students short, so round up to 1690.
When you must have enough, you always round up — a partial pack still has to be bought as a whole pack.
4.OA.A.3Identify SubproblemsThe notebooks bought have to be rounded up to 1690, not down to 1680.
Every student has to receive 2 notebooks, so the pile bought can never be smaller than the 1682 that are needed.
Packs hold exactly 10 notebooks each, so the pile is a whole number of packs, and 168 packs fall short of 1682 while 169 packs clear it.
1690 is exactly 169 packs of ten, more than the 1682 that are needed.
Dividing by 10 just drops a zero, so it is easy to see 1690 splits cleanly into 169 packs while 1680 would be 1 pack too few.
4.NBT.B.6Analyze The UnitsWhen you must have enough, round UP to the next full pack — a leftover few still needs one more whole pack.