Adding within 100
In 2nd grade, children learn to add numbers when the total is 100 or less, such as 47 + 38, by working with tens and ones in flexible ways.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 2nd grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
What is 10 + 25 + 5?
- 30
- 40
- 45
Why this matters
Adding with confidence gives your child a solid base for almost all the math to come. Sums within 100 lead to adding within 1,000 later this year, then to multi-step problems, money, and time in 3rd grade. They also help your child notice when an answer is off, such as a total that is smaller than one of the numbers added. And it comes up everywhere: counting coins, totaling game scores, and adding up prices at the store.
Next comes subtracting within 100, which builds on what your child learns here.
Where kids can get stuck
- 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.
How you can help
- Add up prices together at the store. If one item costs 38 cents and another costs 45 cents, ask your child to find the total, and let them take their time.
- Keep score in a family game and ask your child to add each round in their head, saying the tens first and then the ones. For 26 and 35, that is 20 and 30, then 6 and 5.
- Ask "how many in all?" during the day. If you read 28 pages this morning and 35 at bedtime, how many is that? Then ask how they figured it out.
The kid-friendly video below explains it in a few minutes, and Bobby's Math Club offers free practice that grows with your child.
Kid-friendly explanation
Questions parents ask
Why is my child learning several ways to add instead of one method?
Different problems are easier with different strategies. Jumping by tens works well for 47 + 30, while breaking numbers into tens and ones works well for 47 + 38. Knowing several strategies helps your child understand numbers more deeply, catch mistakes, and do mental math. The standard written method comes later, in 4th grade, built on this understanding.
Should I teach my child to carry the one?
It is best to follow the strategies your child is learning at school, since teaching a different method can be confusing. If your child already carries the one, ask them to explain why it works using tens and ones: 7 and 8 make 15, which is one ten and five ones. Understanding the reason matters more than which method is used.
What does fluent mean for adding within 100?
Fluent means your child can add numbers within 100 accurately, efficiently, and flexibly. They do not need to answer instantly or without paper. A fluent child picks a sensible strategy, works through it without getting lost, and can explain or check their answer. Speed tends to come as the strategies become familiar.
Make learning math fun
Bobby's Math Club turns 2nd grade math practice into something fun to do together.
- Free, unlimited practice for every child in your family
- Questions matched to your child’s level, a few minutes a day
- Hints when they are stuck, and a celebration when it clicks
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.
Ready to watch your child’s confidence grow?
Your 2nd grade child can start today with free, unlimited practice that grows with them.
Join the clubNote for teachers: This skill is covered by Common Core math standard 2.NBT.B.5: “Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.” Learn how Bobby's Math Club can help your students grow. (Common Core 2.NBT.5)