Illustrative Mathematics Grade 2, Unit 2: Adding and Subtracting Within 100
In this unit, your child adds and subtracts within 100, using tens and ones, base-ten blocks, and drawings. They decide when a ten needs to be broken into 10 ones and compare different strategies for the same problem. Story problems give the numbers meaning. Measuring length comes next, where these sums and differences help compare lengths.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 2?
- Solving one-step story problems within 100, including compare problems, and showing them with drawings and equations. Learn more: One- and two-step story problems within 100
- Adding and subtracting within 100 with base-ten drawings, breaking a ten into 10 ones when the ones run short. Learn more about adding within 100: Adding within 100 · Learn more about subtracting within 100
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 80 minus 20?
- 50
- 60
- 70
How you can help
- Ask a quick question at the store, such as "We need 50 napkins and have 32. How many more?" and let your child explain their thinking.
- Bundle straws or sticks into tens with a hair tie, then use them to show 63 − 28, unbundling a ten when needed.
- Solve one problem two ways together, like 47 + 25 by adding tens first and by making a ten, and compare.
Where kids can get stuck
- Subtracting 1 − 6 as 6 − 1 in the ones place, so 71 − 46 becomes 35.
- Unbundling a ten but forgetting to remove it from the tens, so the answer is 10 too big.
- Picking addition for a compare story because it says "more," then adding the two numbers.
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
- tens
- Groups of 10. In 47, the 4 means 4 tens, or 40.
- ones
- Single units. In 47, the 7 means 7 ones.
- base-ten blocks
- Blocks for ones, tens, and hundreds that help children build and see numbers.
- regroup
- Trading 10 ones for 1 ten, or 1 ten for 10 ones, to add or subtract.
- sum
- The answer when you add numbers together.
- difference
- The answer when you subtract; it also tells how much more one amount is.
- compare
- To decide which is more, less, longer, or shorter, and by how much.
- equation
- A number sentence with an equal sign, like 9 + 4 = 13.
Want to help your child master two-digit math?
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.
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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 2 cover?
Illustrative Mathematics Grade 2 Unit 2 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.