Add 1-and 2-digit numbers mentally (3 addends)

Students can look for pairs that make 10 first, then add the third number — or add left to right, keeping a running total mentally.

Multi-addend problems appear frequently in real-life contexts and word problems, so mental fluency with three numbers at once builds practical arithmetic speed.

The commutative and associative properties mean any order gives the same result — students should choose the order that makes mental calculation easiest, such as combining compatible numbers first.