Maryland Math 2.NOS.C.9.b
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.
Use strategies based on place value (counting on, partial sums, making tens, etc.) to add and subtract.
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 add and subtract by working with tens and ones. They may count on, break numbers apart, or make a ten, then show how their steps work.
What Mastery Looks Like
- A student can solve 47 + 28 by making 50 + 25. They can solve 63 - 27 by subtracting 20, then 7, and explain each step with a drawing or number line.
Common Misconceptions
- Students may add tens to ones, such as treating 40 + 7 as 11. When subtracting, they may try to take 7 ones from 3 ones without trading a ten.
How to Assess It
- Exit ticket: Solve 47 + 28 and 63 - 27. Show your steps with tens and ones or a number line, then explain one step in words.
Lesson moves
Ways to Teach It
Build 52 with base-ten blocks, trade one ten for ten ones, remove 18, and record what remains.
Ask, “Why does 48 + 27 equal 50 + 25?” Have partners explain the move with a tens-and-ones sketch.
Give partners two-digit number cards; they add each pair by counting on tens, then ones, and check each other's number lines.
A class collected 64 cans and donated 28; students draw tens and ones to find how many cans remain.
Free download
Printable 2.NOS.C.9.b Worksheet
A ready-to-print activity worksheet aligned to 2.NOS.C.9.b, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
Download the worksheetKeep exploring
Related Standards
- 2.NOS.C.8.a
Use strategies based on counting (e.g., counting on, counting back) and place value (e.g., partial sums, making tens, etc.) to add and subtract.
- 1.NOS.E.10.b
Use counting strategies and strategies based on place value (e.g., partial sums, making tens, etc.) to add.
- 2.NOS.B.6.a
Use counting, make ten, and ten more/less, doubling strategies to add and subtract.
- 5.NOS.B.7.c
Use strategies based on place value (e.g., partial products, partial quotients) to multiply and divide.
Turn this exact standard into a lesson
Grade, subject, topic, and the complete standard are prefilled. Create one free, no account needed.
Also for this standard:Make a WorksheetMake a QuizMake a Sub Lesson