Into Math Grade 2, Unit 3: Two-Digit Addition and Subtraction
In this unit, your child adds and subtracts two-digit numbers within 100. They break numbers into tens and ones, regroup when needed, add up to four numbers at once, and add or subtract 10 and 100 in their heads. They also explain why their strategies work. It builds on place value and leads into three-digit addition and subtraction.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 3?
- Adding and subtracting within 100, like 47 + 38 or 82 - 56, by breaking numbers into tens and ones. Learn more about adding within 100: Adding within 100 · Learn more about subtracting within 100
- Adding three or four two-digit numbers, like 36 + 14 + 25, by looking for friendly pairs that make tens. Learn more: Adding up to four two-digit numbers
- Adding or subtracting 10 or 100 in their heads, and seeing which digit changes and which digits stay the same. Learn more: Adding or taking away 10 or 100 mentally
- Explaining why a strategy works, such as why regrouping 10 ones as 1 ten keeps the total the same. 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 10 + 25 + 5?
- 30
- 40
- 45
How you can help
- Add up a short list of prices under a dollar, like 36¢, 14¢, and 25¢. Ask your child which two to add first to make it easier.
- Play 'ten more, ten less' on a walk: you say 47, and your child says 57 and 37. Switch roles so they get to quiz you.
- Ask 'How did you get that?' after your child solves 47 + 38. Listen for tens and ones, like 'I added 40 and 30, then 7 and 8.'
Where kids can get stuck
- Forgetting to add the new ten, so 47 + 38 comes out as 75 instead of 85.
- Subtracting the smaller digit from the larger in each place, so 82 - 56 becomes 34.
- Saying 'I carried the one' without knowing that the one is really a ten.
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
- To trade 10 ones for 1 ten, or 10 tens for 1 hundred, and back again.
- addend
- One of the numbers you add. In 8 + 5 = 13, the addends are 8 and 5.
- sum
- The answer when you add. In 8 + 5 = 13, the sum is 13.
- difference
- The answer when you subtract. In 13 - 5 = 8, the difference is 8.
- tens
- Groups of ten. The 4 in 45 means 4 tens, or 40.
- ones
- Single units. The 5 in 45 means 5 ones.
- strategy
- A plan or way to solve a problem.
- mentally
- In your head, without writing it down.
Ready to build your child’s confidence with two-digit addition and subtraction?
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 Into Math Grade 2 Unit 3 cover?
Into Math 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.