Illustrative Mathematics Grade 1, Unit 3: Adding and Subtracting Within 20
In this unit, first graders add and subtract within 20 using what they know about ten. They make a ten, use doubles, and add in whatever order is easiest, and they practice explaining their strategies. It builds on the story problems from the last unit, and next they learn about numbers to 99, where tens and ones become the key to bigger numbers.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 3?
- Solving story problems within 20 and choosing a strategy, like making ten, that fits the numbers. Learn more: Adding and subtracting story problems within 20
- Using the order of addends to make work easier, like turning 3 + 9 into 9 + 3. Learn more: Adding in any order to make it easier
- Adding and subtracting within 20 by making a ten, using doubles, and thinking of 10 and some more. Learn more about adding within 20: Adding within 20 · Learn more about subtracting within 20
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
I had some toy cars. My friend gave me 3 more cars. Now I have 8 cars in total. How many toy cars did I have at first?
- 3
- 5
- 8
How you can help
- Play "close to ten" with playing cards: each player picks two cards and adds, trying to land on 10 or as close as possible. Ask your child how they added.
- Lay out 8 spoons and 6 forks and ask how many in all. Show how moving 2 forks to the spoons makes 10, plus the 4 forks left over.
- Ask doubles questions on a walk or ride, then follow up with a near double, like "8 + 8 is 16, so what is 8 + 9?"
Where kids can get stuck
- Counting by ones for 9 + 7, which is slow and leads to errors.
- Making ten in 8 + 6 but then adding the whole 6 again afterward.
- Thinking 9 + 3 and 3 + 9 are different facts that each need solving.
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
- make a ten
- Split a number to fill a ten first, like 8 + 5 = 8 + 2 + 3.
- doubles
- A number added to itself, like 6 + 6.
- near doubles
- A fact one away from a double, like 6 + 7.
- addend
- A number being added, like 3 and 4 in 3 + 4.
- sum
- The answer when you add, like 7 in 3 + 4 = 7.
- difference
- The answer when you subtract, like 2 in 9 - 7 = 2.
- strategy
- A plan or smart way to solve a problem.
Want to help your child master adding within 20?
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 1 Unit 3 cover?
Illustrative Mathematics Grade 1 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.