Illustrative Mathematics Grade 3, Unit 3: Wrapping Up Addition and Subtraction Within 1000
In this unit, your child adds and subtracts numbers up to 1,000 using place value strategies and written methods. They round to the nearest 10 and 100 to estimate, solve two-step problems, and look for patterns in addition. It follows the area unit and wraps up adding and subtracting before multiplication and division return in the next unit.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 3?
- Rounding to the nearest 10 and 100 on a number line, and using rounded numbers to make a quick estimate. Learn more: Rounding to the nearest 10 or 100
- Using place value to add and subtract within 1,000, comparing methods like base-ten drawings and written algorithms, step-by-step methods. Learn more about adding within 1,000: Adding within 1,000 · Learn more about subtracting within 1,000
- Solving two-step problems with addition and subtraction, and using estimates to decide whether an answer makes sense. Learn more: Story problems with two steps
- Noticing patterns in sums, like why adding two odd numbers always gives an even number. Learn more: Spotting patterns in times tables
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 43 rounded to the nearest 10?
- 50
- 40
- 30
How you can help
- Ask your child to estimate a two-item total by rounding, such as $47 and $28 to $50 and $30, then find the exact total ($75).
- Ask your child to show two different ways to work out 403 − 178, such as counting up or regrouping, and say which they prefer (225).
- Add pairs of odd numbers together, like 7 + 9 or 15 + 13, and ask your child why the sum always comes out even.
Where kids can get stuck
- Taking 3 from 8 in the ones column of 403 − 178 instead of regrouping, and ending up with 375.
- Rounding 65 down to 60, unsure which way the halfway number goes.
- Adding when a two-step story needs subtracting for the second step.
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
- round
- To change a number to a nearby number that is easier to use.
- estimate
- A number close to the exact answer that you find quickly.
- place value
- The value of a digit because of where it is in a number.
- algorithm
- A set of steps you follow the same way every time to solve a problem.
- regroup
- To trade 10 ones for 1 ten, or 10 tens for 1 hundred, and back.
- sum
- The answer to an addition problem.
- difference
- The answer to a subtraction problem.
- odd number
- A number that cannot be split into two equal whole-number groups.
- even number
- A number ending in 0, 2, 4, 6, or 8.
Ready to build your child’s confidence with adding and subtracting within 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.
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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 3 Unit 3 cover?
Illustrative Mathematics Grade 3 Unit 3 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.