Montana Math MT.2.NBT.5

Math2nd GradeNumber and Operations in Base Ten

The Standard

Flexibly, accurately, and efficiently add and subtract within 100 using multiple strategies.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Students add and subtract two-digit numbers using methods such as breaking apart tens and ones, making a ten, or counting up. They choose a method that fits the numbers and check that the answer makes sense.
What Mastery Looks Like: A student can solve 47 + 28 by making a ten or adding tens and ones to get 75. They can solve 63 − 27 by counting up or subtracting in parts to get 36, and explain their steps.
Common Misconceptions: Some students subtract the smaller digit from the larger digit in each place, giving 44 for 63 − 27. Others forget to trade ten ones for one ten when adding, or count the starting number twice when counting up.
How to Assess It: Give an exit ticket: “Solve 63 − 27 two ways. Circle the way you would use again and tell why.”

Lesson moves

Build 47 + 28 with base-ten blocks, trade ten ones for a ten, and record each step on paper.
Ask partners to solve 63 − 27 by counting up and by subtracting 20 then 7, then compare the steps.
Deal four digit cards to make two two-digit numbers whose sum is under 100; add them and check by subtraction.
Set up a class store with items priced at 34¢ and 28¢; find the total and change from 100¢.

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