i-Ready Classroom Mathematics Grade 2, Unit 2: Numbers Within 100
In this unit, your child adds and subtracts two-digit numbers within 100. They use tens and ones, number lines, and regrouping, and add up to four numbers at once. They apply it all to one- and two-step word problems. Next, the numbers grow to 1,000, where the same tens-and-ones thinking extends to hundreds.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 2?
- Solving one- and two-step word problems within 100 with bar models and equations, checking that each answer makes sense. Learn more: One- and two-step story problems within 100
- Adding and subtracting within 100 by tens and ones, on an open number line, or by regrouping. Learn more about adding within 100: Adding within 100 · Learn more about subtracting within 100
- Adding three or four two-digit numbers by finding pairs that make tens, such as 17 + 23 = 40. Learn more: Adding up to four two-digit numbers
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
What is 80 minus 20?
- 50
- 60
- 70
How you can help
- Add up a few items on a receipt and ask your child to find two prices that make an even ten first.
- Count back by tens and then by ones together to show 85 − 22 on a walk: 85, 75, 65, 64, 63. Then let your child pick a problem.
- Make up a two-step story at the park: "23 kids were playing, 8 went home, then 15 more came. How many now?"
Where kids can get stuck
- Mixing up the direction on a number line, jumping forward when the story takes away.
- Writing 13 ones as 13 in the ones place instead of regrouping one ten.
- Using the wrong number in the second step of a two-step problem.
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
- regroup
- Trading 10 ones for 1 ten, or 1 ten for 10 ones, to add or subtract.
- open number line
- A number line with no marks printed, where you draw only the jumps you need.
- tens
- Groups of 10. In 47, the 4 means 4 tens, or 40.
- ones
- Single units. In 47, the 7 means 7 ones.
- addend
- Each number being added. In 5 + 3 = 8, the addends are 5 and 3.
- bar model
- A drawing of bars that shows the parts and the whole in a story problem.
- sum
- The answer when you add numbers together.
- difference
- The answer when you subtract; it also tells how much more one amount is.
Want to help your child master math within 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.
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 i-Ready Classroom Mathematics Grade 2 Unit 2 cover?
i-Ready Classroom Mathematics Grade 2 Unit 2 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.