Montana Math MT.2.NBT.8

Math2nd GradeNumber and Operations in Base Ten

The Standard

Using place value, add or subtract 10 or 100 from a given number.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Students add or subtract 10 or 100 by tracking tens and hundreds. They trade between places when needed, rather than counting by ones.
What Mastery Looks Like: A student can find 295 + 10 = 305 and explain why the hundreds digit changes. They can also show that 304 - 10 = 294 by trading one hundred for ten tens.
Common Misconceptions: Students may write 295 + 10 as 205 because they change only the tens digit. They may say 304 - 10 is 304 because there are no tens to take away.
How to Assess It: Exit ticket: Start at 295. Add 10, then subtract 100. Write both results and explain which digits changed at each step.

Lesson moves

Build 295 with base-ten blocks, add one ten rod, then trade ten rods for one hundred flat.
Ask pairs, 'Why does 304 - 10 equal 294 instead of 304?' Have them sketch the trade and explain it.
Start at 550, draw four cards marked +10, -10, +100, or -100, and record the number after each draw.
Post a library count of 395 books, then find the count after 100 arrive and 10 are checked out.

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