Maryland Math 1.NOS.E.10.c

Math1st GradeNumber and Operation Sense

The Standard

1.NOS.E.10: Add within 100 including adding a two-digit number and a one-digit number and adding a two-digit number and a multiple of 10. Understand that when adding two-digit numbers, tens are added to tens, ones are added to ones, and sometimes it is necessary to compose or decompose a ten.

Use properties of operations, and/or the inverse relationship between addition and subtraction to add.

Maryland College and Career Ready Standards for Mathematics (2025) · USE PLACE VALUE UNDERSTANDING AND PROPERTIES TO ADD AND SUBTRACT.

Teacher's field guide

What Students Need to Do: Students add by switching the order of numbers, making a ten, or using a related subtraction fact. They show their thinking with counters, drawings, or equations.
What Mastery Looks Like: A student solves 8 + 7 by moving 2 from the 7 to make 10, then adding the remaining 5. They also know that 14 − 6 = 8 means 6 + 8 = 14.
Common Misconceptions: Some students think switching 6 + 9 to 9 + 6 changes the total. Others move 2 from 7 to 8 but still add all 7. Some write 14 + 6 = 8 after seeing 14 − 6 = 8.
How to Assess It: Exit ticket: Solve 9 + 7 by making 10. Write a subtraction fact that checks your answer.

Lesson moves

Give students 8 counters and 7 counters; have them move 2 to make a group of 10 and record 10 + 5.
Ask students to write why 7 + 9 and 9 + 7 have the same total without counting both sums.
Play a matching game with cards such as 12 − 5 = 7 and 5 + 7 = 12.
Set out 9 cups, then 6 more; move 1 cup to make a group of 10 and find the total.

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