Montana Math MT.1.NBT.5

Math1st GradeNumber and Operations in Base Ten

The Standard

Using place value, given a two-digit number, find 10 more or 10 less than the number.

2026 Montana Mathematics Content Standards

Teacher's field guide

What Students Need to Do: Given a two-digit number, students find the number 10 more and the number 10 less. They use tens and ones to explain why the ones digit stays the same.
What Mastery Looks Like: For 46, a student says 56 is 10 more and 36 is 10 less. They can show each change with ten-sticks or a place-value drawing without counting by ones.
Common Misconceptions: Students may change the ones digit and say 10 more than 46 is 47. They may count backward by ones and say 10 less than 40 is 39.
How to Assess It: Write 64 on the board. Ask students to write 10 more and 10 less, then circle the digit that stayed the same in all three numbers.

Lesson moves

Give pairs ten-sticks and cubes to build 46, then add or remove one ten-stick and record each new number.
Write 73, 83, and 63 on the board; ask partners to explain which is 10 more and which is 10 less than 73.
Give pairs two-digit number cards; one student draws a card, and the other writes 10 more and 10 less.
Show a toy priced at 45 cents; ask its price after a 10-cent increase or a 10-cent decrease.

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