2.NBT.B.6

Add up to four two-digit numbers using strategies based on place value and properties of operations.

Add up to four two-digit numbers. Knowing that addition is commutative and associative means we can add in any order we like. By changing the order in which we add, we can sometimes make the problem easier to solve. For example, 37 + 25 + 13 can be rearranged to 37 + 13 + 25.