Bridges in Mathematics Grade 2, Unit 3: Addition & Subtraction Within One Hundred
In this unit, your child adds and subtracts two-digit numbers within 100, using tens and ones to regroup, which means trading 10 ones for a ten or a ten for 10 ones. They add lists of up to four numbers, solve story problems, and explain why their strategies work. Next, these skills get used to measure, compare, and show data.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 3?
- Solving story problems within 100, including two-step ones, by drawing a bar or number line and writing an equation. Learn more: One- and two-step story problems within 100
- Adding and subtracting numbers like 47 + 38 and 82 − 56, regrouping when the ones run short or overflow. Learn more about adding within 100: Adding within 100 · Learn more about subtracting within 100
- Adding three or four two-digit numbers, looking for friendly pairs like 36 + 14 that make an even ten. Learn more: Adding up to four two-digit numbers
- Explaining in words or drawings why a strategy works, such as why the "carried 1" is really a ten. Learn more about explaining why addition strategies work: Explaining why addition strategies work · Learn more about explaining why subtraction strategies work
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 short grocery list of prices under a dollar, like 25, 18, and 32 cents, and ask your child which two to add first and why.
- Keep score in a board or card game and have your child add each turn's points, saying the tens and ones out loud as they go.
- Ask "How did you know?" after your child solves a problem like 52 − 27, and let them show you with a quick sketch of tens and ones.
Where kids can get stuck
- Subtracting the smaller digit from the larger one, so 82 − 56 becomes 34 instead of 26.
- Forgetting the extra ten, answering 75 instead of 85 for 47 + 38.
- Dropping one of the numbers when adding four in a row, so the total comes out too small.
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.
- sum
- The answer when you add numbers together.
- difference
- The answer when you subtract; it also tells how much more one amount is.
- addend
- Each number being added. In 5 + 3 = 8, the addends are 5 and 3.
- tens
- Groups of 10. In 47, the 4 means 4 tens, or 40.
- ones
- Single units. In 47, the 7 means 7 ones.
- equation
- A number sentence with an equal sign, like 9 + 4 = 13.
- strategy
- A way of solving a problem, like making a ten or counting on.
Want to help your child master adding and subtracting 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.
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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 Bridges in Mathematics Grade 2 Unit 3 cover?
Bridges in Mathematics Grade 2 Unit 3 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.