2nd Grade · Number & Operations in Base Ten
2.NBT.B.7: Add and subtract within 1000
2.NBT.B.7 is a 2nd grade Common Core math standard in Number & Operations in Base Ten. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in 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.
In plain words
Add and subtract within 1000.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 6
What is the sum of 215 and 68?
- 283
- 273
- 383
Where students can get stuck
Add within 1000.
- Writing each column's total straight into the answer, so 365 + 248 becomes 51013 instead of 613.
- Forgetting the new hundred made from the tens, so 271 + 154 comes out as 325 instead of 425.
- Lining the numbers up by their first digit, so 352 + 41 is added as 352 + 410 and gives 762.
Subtract within 1000.
- Taking the top digit from the bottom one when the top is smaller, so 402 - 175 becomes 373.
- Checking by adding the two starting numbers, 402 + 175, instead of adding the answer back to 175.
- Breaking apart a ten but forgetting to lower the tens digit, so 352 - 128 comes out as 234 instead of 224.
Effective teaching strategies
- Use base-ten blocks for 305 - 148, trading 1 hundred for 10 tens and then 1 ten for 10 ones, and have students say each trade out loud.
- Have students add 276 + 158 with blocks, trading 10 ones for a ten and 10 tens for a hundred, and name the place whose total they are writing at each step.
- Ask students to record each block trade in the written method, such as a small 1 above the tens column, and check a subtraction by adding the answer to the amount taken away.
Units that teach this standard
Find where 2.NBT.B.7 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Eureka Math
Everyday Mathematics
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Each skill has its own guide for families, with a plain-language look at the skill, three questions to try together, and ideas for helping at home.
Help every student practice place value at home
In Bobby's Math Club, students practice at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free for every family.
See how it works for teachers
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.