Reveal Math Grade 2, Unit 8: Three-Digit Subtraction
In this unit, your child subtracts three-digit numbers within 1,000. They regroup a hundred as ten tens and a ten as ten ones, subtract 10 or 100 in their heads, and explain each step with drawings. It builds on three-digit addition from the last unit and leads into money and time, where subtracting helps with making change.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 8?
- Subtracting three-digit numbers, like 402 - 175, including regrouping across a zero by trading a hundred for 10 tens. Learn more about adding within 1,000: Adding within 1,000 · Learn more about subtracting within 1,000
- Subtracting 10 or 100 from numbers between 100 and 900 in their heads, like knowing 100 less than 815 is 715. Learn more: Adding or taking away 10 or 100 mentally
- Explaining why trading a hundred for 10 tens keeps the number the same, using a drawing or blocks. 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
A toy store had 450 toy cars and sold 120 of them. How many toy cars are left?
- 320
- 570
- 330
How you can help
- Find how many pages are left in a long book, such as 402 pages with 175 read. Let your child explain how they traded a hundred.
- Play '100 less' on a walk or ride with numbers like 815. Then try 10 less, like 810 to 800, and talk about which digit changed.
- Check a subtraction answer by adding: if 402 - 175 = 227, add 227 + 175 together and see if you get 402.
Where kids can get stuck
- Subtracting the smaller digit from the larger in every place, so 402 - 175 becomes 373.
- Getting stuck on the zero in 402, unsure how to make tens before making ones.
- Changing the tens digit instead of the hundreds when finding 100 less, saying 805 for 815.
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
- difference
- The answer when you subtract. In 13 - 5 = 8, the difference is 8.
- regroup
- To trade 10 ones for 1 ten, or 10 tens for 1 hundred, and back again.
- decompose
- To break a number into parts, like 82 = 80 + 2, or 1 hundred into 10 tens.
- hundred
- Ten tens, or 100. The 7 in 706 means 7 hundreds.
- digit
- One of the symbols 0 to 9 used to write numbers. 352 has three digits.
- mentally
- In your head, without writing it down.
Ready to build your child’s confidence with three-digit subtraction?
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 Reveal Math Grade 2 Unit 8 cover?
Reveal Math Grade 2 Unit 8 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.