Into Math Grade 2, Unit 4: Three-Digit Addition and Subtraction
In this unit, your child adds and subtracts three-digit numbers within 1,000. They use models, drawings, and written steps, regroup tens and hundreds, add or subtract 10 and 100 in their heads, and explain why each step works. This builds on two-digit addition and subtraction and leads into money and time, where those skills get real use.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 4?
- Adding and subtracting within 1,000, like 365 + 248 or 402 - 175, by working with hundreds, tens, and ones. Learn more about adding within 1,000: Adding within 1,000 · Learn more about subtracting within 1,000
- Finding 10 more, 10 less, 100 more, or 100 less than a number from 100 to 900 without writing anything down. Learn more: Adding or taking away 10 or 100 mentally
- Explaining why trading 1 hundred for 10 tens works, using a drawing or blocks to show it. 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
- Add two three-digit numbers from a game score or a book's page count, like 365 and 248. Ask your child to add the hundreds, then the tens, then the ones.
- Quiz each other on a ride: 'What is 100 more than 293? What is 10 more?' Notice together what happens when the tens digit is 9.
- Ask your child to teach you how they solved 402 - 175. Let them draw hundreds as squares, tens as lines, and ones as dots.
Where kids can get stuck
- Writing each column's total into the answer, so 365 + 248 becomes 51013 instead of 613.
- Getting stuck when the tens digit is 9, answering 2103 for 10 more than 293 instead of 303.
- Struggling to regroup across a zero in 402 - 175, where a hundred must become 10 tens first.
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
- hundreds
- Groups of 100. The 3 in 352 means 3 hundreds, or 300.
- regroup
- To trade 10 ones for 1 ten, or 10 tens for 1 hundred, and back again.
- compose
- To put parts together to make a bigger unit, like 10 tens making 1 hundred.
- decompose
- To break a number into parts, like 82 = 80 + 2, or 1 hundred into 10 tens.
- digit
- One of the symbols 0 to 9 used to write numbers. 352 has three digits.
- sum
- The answer when you add. In 8 + 5 = 13, the sum is 13.
- difference
- The answer when you subtract. In 13 - 5 = 8, the difference is 8.
Want to help your child master three-digit addition and 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.
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 Into Math Grade 2 Unit 4 cover?
Into Math Grade 2 Unit 4 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.