Reveal Math Grade 1, Unit 9: Two-Digit Addition and Subtraction
In this unit, your child uses tens and ones to add and subtract bigger numbers. They add a two-digit number and a one-digit number, find 10 more and 10 less, and subtract tens like 50 - 20. This builds on last unit's tens and ones and leads into collecting and reading data.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 9?
- Adding within 100, like 47 + 6 and 52 + 30, by putting tens with tens, ones with ones, and making a new ten. Learn more: Adding two-digit numbers within 100
- Finding 10 more and 10 less than a number like 64 without counting by ones. Learn more: 10 more or 10 less in your head
- Subtracting multiples of ten, like 90 - 60, by thinking of tens, and explaining how they solved it. Learn more: Subtracting tens, like 70 - 30
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
If you have 2 tens and 4 ones, and then you get 5 more ones, how many do you have in total?
- 30
- 29
- 28
How you can help
- Use straw bundles to show 47 + 6. Put the loose straws together, make a new bundle of ten, and count the total.
- Say a number at the bus stop or on a walk, like 64. Ask for 10 more, then 10 less, and talk about which digit changed.
- Ask about tens while cleaning up: "There are 50 blocks on the floor. We put 20 away. How many are left?" Let your child explain it with tens.
Where kids can get stuck
- Lining up 6 under the 4 in 47 + 6 and getting 107 instead of 53.
- Saying 10 more than 64 is 65, because adding seems to change the last digit.
- Writing 3 for 90 - 60, forgetting that the answer is 3 tens, or 30.
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 ten. In 34, the 3 means 3 tens.
- ones
- Single units. In 34, the 4 means 4 ones.
- new ten
- Ten ones grouped together to make one ten when adding.
- sum
- The answer when you add numbers together.
- 10 more
- The number you get by adding one ten, like 47 to 57.
- 10 less
- The number you get by taking away one ten, like 47 to 37.
- multiple of 10
- A number you reach by counting by tens, like 30, 60, or 90.
Ready to build your child’s confidence with two-digit adding and subtracting?
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 1 Unit 9 cover?
Reveal Math Grade 1 Unit 9 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.