Montana Math MT.2.NBT.9

Math2nd GradeNumber and Operations in Base Ten

The Standard

Understand and make connections between different strategies for addition and subtraction.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Students solve addition and subtraction problems in more than one way. They explain how the steps in each method lead to the same answer.
What Mastery Looks Like: A student can solve 38 + 27 by splitting tens and ones or by making 40, and get 65 both ways. They can solve 52 - 28 by subtracting in parts or counting up, then explain why both give 24.
Common Misconceptions: Some students make 40 from 38 but forget to take 2 from 27. Others subtract the smaller digit from the larger in each column and get 36 for 52 - 28.
How to Assess It: Exit ticket: Solve 52 - 28 by subtracting 20 then 8, and by counting up from 28. Show how each method gives 24.

Lesson moves

Build 38 + 27 with tens rods and ones cubes, then find 65 on an open number line using jumps of 20 and 7.
Show 52 - 20 - 8 and jumps from 28 to 30 to 50 to 52; ask how each gives 24.
Give pairs cards showing 46 + 18, 40 + 10 + 6 + 8, and 46 + 4 + 14; have them match and explain.
Post a $36 book and a $28 game; students total a pretend receipt by splitting tens and ones, then by making 40.

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