Go Math! Grade 1, Chapter 8: Two-Digit Addition and Subtraction
In this unit, first graders add and subtract with two-digit numbers. They add tens and ones within 100, making a new ten when the ones reach 10, find 10 more and 10 less in their heads, and subtract tens, as in 70 - 30. It builds on comparing numbers from the last unit, and next they move on to measuring length and telling time.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Chapter 8?
- Adding a two-digit number and a one-digit number or a multiple of ten, like 52 + 6 or 52 + 30. Learn more: Adding two-digit numbers within 100
- Finding 10 more and 10 less than a number mentally, like 64 and 54, and explaining which digit changes. Learn more: 10 more or 10 less in your head
- Subtracting multiples of ten, such as 70 - 30, using tens models and related addition. 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
- Show 52 with 5 bundles of ten straws and 2 loose ones, then add 30 by adding 3 bundles. Ask how many tens and ones there are now.
- Play "10 more, 10 less" at the store with prices: "This costs 64 cents. What would 10 cents more be? 10 cents less?"
- Count back by tens from 70 together on a walk, then ask what 70 - 30 is. Ask whether the answer is 4 or 40, and how they know.
Where kids can get stuck
- Adding the 6 to the tens in 52 + 6 and getting 112 instead of 58.
- Changing the ones digit for 10 more, so 10 more than 64 becomes 65.
- Answering 4 for 70 - 30, forgetting that the answer is 4 tens.
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, there are 3 tens.
- ones
- Single things not in a group of ten. In 34, there are 4 ones.
- sum
- The answer when you add, like 7 in 3 + 4 = 7.
- difference
- The answer when you subtract, like 2 in 9 - 7 = 2.
- make a ten
- Split a number to fill a ten first, like 8 + 5 = 8 + 2 + 3.
- 10 more
- The number you get by adding one ten, like 46 to 56.
- 10 less
- The number you get by taking away one ten, like 46 to 36.
- multiple of 10
- A number you say when counting by tens, like 30 or 70.
Ready to build your child’s confidence with two-digit adding?
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 Go Math! Grade 1 Chapter 8 cover?
Go Math! Grade 1 Chapter 8 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.