Illustrative Mathematics Grade 2, Unit 7: Adding and Subtracting Within 1000
In this unit, your child adds and subtracts within 1,000, using base-ten blocks, number lines, and written methods that regroup hundreds, tens, and ones. They add up to four two-digit numbers, add or take away 10 and 100 in their head, and explain why their strategies work. Next, the year turns to equal groups, a first step toward multiplication.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 7?
- Adding up to four two-digit numbers, looking for pairs that make a ten or a hundred. Learn more: Adding up to four two-digit numbers
- Adding and subtracting within 1,000 with blocks, number lines, and written methods, composing or decomposing a ten or a hundred. Learn more about adding within 1,000: Adding within 1,000 · Learn more about subtracting within 1,000
- Finding 10 or 100 more or less than any number from 100 to 900 in their head. Learn more: Adding or taking away 10 or 100 mentally
- Explaining why their strategies work and comparing them with other ways to solve the same problem. Learn more about explaining why addition strategies work: Explaining why addition strategies work · Learn more about explaining why subtraction strategies work
Sample questions to try together
These are real questions from our 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 5 + 5 + 5 + 5 + 5?
- 20
- 25
- 30
How you can help
- Add the ages of four family members or friends, and ask your child to find two that make a ten first.
- Play a number game with 100s and 10s: start at 350 and take turns adding or taking away 100 or 10.
- Ask your child to solve 432 − 199 with a shortcut, like taking away 200 and giving 1 back, and explain why that works.
Where kids can get stuck
- Taking away 200 instead of 199 and then subtracting 1 more instead of adding it back.
- Leaving out one of four numbers partway through, so the total is short.
- Getting stuck when the tens digit is 9, saying 10 more than 495 is 4105.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- compose
- To put parts together to make a bigger unit, like 10 ones making 1 ten.
- decompose
- To break a number into parts, like 1 hundred into 10 tens.
- hundreds
- Groups of 100. In 706, the 7 means 7 hundreds, or 700.
- regroup
- Trading 10 ones for 1 ten, or 1 ten for 10 ones, to add or subtract.
- number line
- A line with numbers in order at equal spaces, used to count, add, and subtract.
- mentally
- In your head, without writing it down or using objects.
- strategy
- A way of solving a problem, like making a ten or counting on.
Ready to build your child’s confidence with addition and subtraction to 1,000?
In Bobby's Math Club, your child practices these skills 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.
Join the club
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.
Which math standards does Illustrative Mathematics Grade 2 Unit 7 cover?
Illustrative Mathematics Grade 2 Unit 7 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.