Everyday Mathematics Grade 1, Unit 9: Two-Digit Addition and Review
In this unit, your child adds two-digit numbers by putting tens with tens and ones with ones. They find 10 more or 10 less in their head and subtract tens, like 70 - 30. After the geometry and time unit, this final unit pulls together the place value work of first grade and looks ahead to second grade.
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 36 + 7 or 45 + 30, by combining tens with tens and ones with ones, and making a new ten. Learn more: Adding two-digit numbers within 100
- Finding 10 more or 10 less than a two-digit number in their head and explaining why only the tens digit changes. Learn more: 10 more or 10 less in your head
- Subtracting tens from tens, like 80 - 50, by thinking 8 tens take away 5 tens leaves 3 tens. 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
- Count by tens from any number on a walk, like 23, 33, 43, and ask which digit changes each time and which one stays the same.
- Bundle straws into tens and show 36. Add 7 loose straws, then make a new bundle of ten from the loose ones and count the total.
- Ask quick tens questions at dinner, like "You have 70 points and lose 30. How many are left?" Let your child explain using tens.
Where kids can get stuck
- Writing down all 13 ones in 36 + 7 instead of making a new ten, getting 313.
- Changing the ones digit for 10 more, saying 10 more than 34 is 35.
- Forgetting the zero, writing 4 as the answer to 70 - 30 instead of 40.
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.
- tens digit
- The digit on the left in a two-digit number, telling how many tens.
- 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 addition?
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 Everyday Mathematics Grade 1 Unit 9 cover?
Everyday Mathematics 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.