Subtracting tens, like 70 - 30
In 1st grade, children learn to subtract tens from tens, as in 70 - 30 = 40; to show it with models; and to explain how their strategy connects to the written problem.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 1st grade 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 60 minus 20?
- 40
- 50
- 80
Why this matters
Subtracting tens lets your child stretch the facts they already know to much bigger numbers: 7 tens take away 3 tens leaves 4 tens, in the same way that 7 - 3 = 4. It is a step toward 2nd grade problems like 74 - 38, where children think about tens and ones separately and sometimes break a ten apart. Without this idea, subtracting larger numbers can feel like a pile of unrelated steps.
Where kids can get stuck
- Forgetting the zero, writing 4 instead of 40 as the answer to 70 - 30.
- Counting back by ones from 70, thirty separate times, instead of counting back by tens: 60, 50, 40.
- Answering 1 instead of 10 for 60 - 50, losing track of the fact that the answer is still in tens.
How you can help
- Use dimes for subtraction. Start with 8 dimes, which is 80 cents, take away 5 dimes, and ask how much is left. Then say the equation together: 80 - 50 = 30.
- Count backward by tens together during bath time or bedtime from 90 down to 0, then ask questions like "If you start at 90 and go back 3 tens, where are you?"
- Connect to facts your child knows: ask "What is 6 - 2?" then "What is 60 - 20?" and let them notice the pattern on their own.
The kid-friendly video below is a nice one to watch together. For more, Bobby's Math Club has free practice at your child’s level.
Kid-friendly explanation
Questions parents ask
Why is my child learning to subtract tens like 70 - 30 this way?
Thinking of 70 - 30 as 7 tens minus 3 tens lets your child use a fact they already know, 7 - 3 = 4, to solve a bigger problem. Using bundles or drawings keeps the meaning clear. This place value thinking makes later subtraction with tens and ones much easier to understand.
Does my child need to borrow or regroup in 1st grade?
No. In 1st grade, subtraction with larger numbers is limited to multiples of 10, like 80 - 20. There are no ones to deal with, so no regrouping is needed. Subtracting numbers like 52 - 17, which require breaking apart a ten, is a 2nd-grade skill.
How do I know if my child really understands this?
A good sign is when your child can explain the answer without counting by ones, for example "90 minus 60 is 30 because 9 tens take away 6 tens is 3 tens." Another is being able to show it with dimes or bundles. Getting the answer by counting back by ones works but shows the place value idea is still forming.
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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.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 1.NBT.C.6: “Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.” Learn how Bobby's Math Club can help your students grow. (Common Core 1.NBT.6)