Maryland Math 2.NOS.C.9.d
The Standard
- 2.NOS.C.9
- Add and subtract within 1000, recognizing that when adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.
Represent and explain the calculation by connecting the strategy used to the meaning of addition and subtraction.
Maryland College and Career Ready Standards for Mathematics (2025) · USE REPRESENTATIONS, PLACE VALUE UNDERSTANDING, AND PROPERTIES OF OPERATIONS TO ADD AND SUBTRACT.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students solve addition and subtraction problems with drawings, number lines, or tens and ones. They explain how each step shows joining, taking away, or finding a difference.
What Mastery Looks Like
- For 38 + 25, a student shows tens and ones, trades 10 ones for a ten, and explains why the total is 63. For 52 - 18, they count up from 18 on a number line and explain why the jumps total 34.
Common Misconceptions
- Students may show 13 ones in a drawing but write 513 instead of trading 10 ones for a ten. They may count up to subtract but not see that the jumps measure the difference between the numbers.
How to Assess It
- Exit ticket: Solve 43 - 17 with a labeled number line or tens-and-ones drawing. Write one sentence explaining how your jumps or blocks show subtraction.
Lesson moves
Ways to Teach It
Give pairs 28 and 15 snap cubes grouped in tens and ones; have them join the groups, regroup, and sketch each step.
Ask, "How can counting up from 27 to 61 show 61 - 27?" Have students draw jumps and explain what their total means.
Play match-up with cards showing equations, base-ten drawings, and number-line jumps; students match sets and explain one match to a partner.
A library has 36 picture books and gets 27 more; students draw tens and ones and explain how they find the new total.
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Printable 2.NOS.C.9.d Worksheet
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Related Standards
- 1.NOS.E.12.c
Represent and explain the calculation by connecting the strategy used to the meaning of subtraction.
- 1.NOS.E.12.b
Use counting strategies, properties of operations, and/or the inverse relationship between addition and subtraction to subtract.
- 1.NOS.E.10.d
Represent and explain the calculation by connecting the strategy used to the meaning of addition.
- 1.NOS.E.13.c
Represent and explain the calculation by connecting the strategy used to the meaning of subtraction.
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