Maryland Math 1.NOS.B.3.c

Math1st GradeNumber and Operation Sense

The Standard

1.NOS.B.3: Extend understanding of 10 as a group, collection, or bundle of ten ones, called a “ten,” to compose and decompose two-digit numbers.

Compose and decompose two-digit numbers in more than one way (e.g. 46 = 41 + 5 or 46 = 23 + 23).

Maryland College and Career Ready Standards for Mathematics (2025) · UNDERSTAND PLACE VALUE AND REPRESENTATIONS OF NUMBERS.

Teacher's field guide

What Students Need to Do: Students split a two-digit number into two parts in several ways. They put different pairs of parts together to make the same number and show their work with blocks, drawings, or equations.
What Mastery Looks Like: Given 46, a student can write 40 + 6, 30 + 16, and 23 + 23. They can show with blocks or a drawing why each pair makes 46.
Common Misconceptions: Some students think 40 + 6 is the only way to split 46. Others forget that trading one ten for ten ones keeps the total the same.
How to Assess It: Exit ticket: Write three different addition equations for 46. Draw tens and ones to prove one equation that does not use 40.

Lesson moves

Give students four ten-rods and six ones; have them trade one rod for ten ones and record 46 as 40 + 6 and 30 + 16.
Ask, 'Can 30 + 16 and 40 + 6 both equal 46?' Have students draw how they know.
Partners draw a number card from 20 to 99, then each writes a different addition equation for that number.
Tell students a class collected 46 cans; have them write two ways to split the cans between two boxes.

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