2nd Grade · Number & Operations in Base Ten
2.NBT.B.5: Fluently add and subtract within 100
2.NBT.B.5 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
Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
In plain words
Fluently add and subtract within 100.
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 10 + 25 + 5?
- 30
- 40
- 45
Where students can get stuck
Fluently add within 100.
- Forgetting the extra ten when the ones add up to more than 9, answering 75 instead of 85 for 47 + 38.
- Adding the tens and the ones separately but never putting the two answers together, so 47 + 38 stays as 70 and 15.
- Counting up one number at a time for every problem, which is slow and easy to lose track of, instead of jumping by tens.
Fluently subtract within 100.
- Subtracting the smaller digit from the larger in each place, so 82 - 56 becomes 34.
- Counting back one number at a time and losing track partway, so 53 - 18 ends up a few away from 35.
- Thinking subtraction only means taking away, so a question like "How many more is 64 than 48?" feels like a different kind of problem.
Effective teaching strategies
- Show 36 + 29 on an open number line by jumping 30 to land on 66 and then back 1, so students see a friendly number can make a problem easier.
- Ask students to solve 74 - 38 two ways, by counting up from 38 to 74 and by taking away tens and ones, and to see that both give 36.
- Mix problems such as 50 + 30, 58 + 6, and 63 - 59, and ask students to say which strategy fits each one before they compute.
Watch our video
A short, kid-friendly lesson on this skill, for the whole class or for students to watch on their own.
Fluently subtract within 100
Units that teach this standard
Find where 2.NBT.B.5 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
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.