Maryland Math 2.NOS.B.6.c

Math2nd GradeNumber and Operation Sense

The Standard

2.NOS.B.6: Recall or quickly derive addition and subtraction facts within 20.

Use the inverse operation to add and subtract (e.g. think of 7 + ? = 15 to solve 15 – 7 = ?).

Maryland College and Career Ready Standards for Mathematics (2025) · ADD AND SUBTRACT WITHIN 20.

Teacher's field guide

What Students Need to Do: Students use an addition fact to solve a related subtraction problem within 20. They find the missing number, then check that it works in both equations.
What Mastery Looks Like: Given 15 − 7, a student thinks, 7 plus what makes 15? They answer 8 and check that 7 + 8 = 15.
Common Misconceptions: Some students subtract the smaller number from the larger one without seeing how addition can help. Others write 15 + 7 when asked to find 15 − 7.
How to Assess It: On an exit ticket, ask: Solve 14 − 6 by writing a related addition equation. Explain how you found the answer.

Lesson moves

Give pairs 15 counters, have them move 7 aside, then write 7 + 8 = 15 and 15 − 7 = 8.
Ask students to draw and explain how 6 + ? = 14 helps them solve 14 − 6.
Make cards with subtraction problems and matching missing-addend equations, then have partners find and solve the pairs.
Put 16 pencils in a cup, remove 9, and ask students to use 9 + ? = 16 to find how many remain.

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