Into Math Grade 1, Unit 5: Two-Digit Addition and Subtraction
In this unit, your child adds and subtracts with bigger numbers using tens and ones. They find 10 more and 10 less in their head, subtract tens like 90 - 40, and add numbers like 47 + 6. This builds on last unit's place value and leads into measuring, telling time, and reading data.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 5?
- Adding a two-digit number and a one-digit number, or a multiple of ten, by adding tens to tens and ones to ones. Learn more: Adding two-digit numbers within 100
- Saying 10 more or 10 less than any two-digit number without counting, such as 46 becoming 56 or 36. Learn more: 10 more or 10 less in your head
- Subtracting multiples of ten, like 90 - 40, with models and drawings, and explaining the strategy used. 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
- Make paper cards worth 10, 20, 30, 40, and 50. Draw two, add them, then take the smaller from the bigger.
- Pick a number at dinner, like 58, and take turns saying 10 more or 10 less. Ask which digit changed and why.
- Line up cups of 10 pasta pieces plus some loose ones to show 47 + 6. Have your child fill a new cup of ten before counting.
Where kids can get stuck
- Counting on by ones, ten separate times, to find 10 more than 56, and often losing count.
- Treating 36 + 20 like 36 + 2 and answering 38, because the zero in 20 seems unimportant.
- Answering 1 instead of 10 for 60 - 50, losing track that the answer is still in 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, the 3 means 3 tens.
- ones
- Single units. In 34, the 4 means 4 ones.
- 10 more
- The number you get by adding one ten, like 47 to 57.
- 10 less
- The number you get by taking away one ten, like 47 to 37.
- multiple of 10
- A number you reach by counting by tens, like 30, 60, or 90.
- new ten
- Ten ones grouped together to make one ten when adding.
- difference
- The answer when you subtract one number from another.
Ready to build your child’s confidence with 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.
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 Into Math Grade 1 Unit 5 cover?
Into Math Grade 1 Unit 5 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.