i-Ready Classroom Mathematics Grade 1, Unit 4: Two-Digit Addition and Subtraction
In this unit, first graders use place value to add and subtract two-digit numbers. They add tens to tens and ones to ones, making a new ten when needed, find 10 more and 10 less mentally, and subtract tens, as in 50 - 20. It builds on tens and ones from the last unit, and next they turn to shapes, time, and measuring length.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 4?
- Adding within 100, like 38 + 5 or 38 + 50, by combining like places and making a new ten from extra ones. Learn more: Adding two-digit numbers within 100
- Finding 10 more or 10 less than a number without counting, such as 73 to 83 or 73 to 63. Learn more: 10 more or 10 less in your head
- Subtracting tens, like 50 - 20, using models, a number chart, or adding up from 20. 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
- Add up two small purchases at the store in your heads, like 38 cents and 5 cents. Ask your child to make a ten from the ones first.
- Count up and down by tens from any number on a walk, like 73, 83, 93, then back down. Ask which digit keeps changing.
- Use bundles of ten straws to show 50 - 20: start with 5 bundles and take 2 away. Ask whether the answer is 3 or 30.
Where kids can get stuck
- Writing 313 for 38 + 5, recording all 13 ones instead of making a new ten.
- Treating 38 + 50 like 38 + 5 and answering 43.
- Answering 3 for 50 - 20, forgetting the answer is 3 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.
Want to help your child master adding and subtracting to 100?
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 i-Ready Classroom Mathematics Grade 1 Unit 4 cover?
i-Ready Classroom Mathematics Grade 1 Unit 4 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.