Explain why subtracting by tens and ones works
Talking through subtraction helps your child trust their own thinking, especially on problems where a ten has to be broken apart. If they can say why 52 - 17 needs a trade, they're less likely to subtract the wrong way round. And the reasons carry forward: the same ideas explain subtracting bigger numbers later this year and next, and checking work with addition for years to come.
In this video, your child will learn to explain why subtracting works.
The lesson stops at each question for your child's answer.
Three problems, each a little harder
Each problem is worked step by step. Your child will solve the last one before Bobby shows how.
Example 1
58 − 23 = ?
Example 2
74 − 38 = ?
Your child's turn
81 − 46 = ?
The three key steps
- 1Numbers are tens and ones.
- 2Ones from ones, tens from tens.
- 3Not enough ones? Break a ten.
Mistakes to listen for
- Saying "you can't take 7 from 2" for 52 - 17, instead of explaining that a ten becomes ten ones to make 12.
- Taking 20 from 45 to find 45 - 19, then taking 1 more away instead of adding it back, and getting 24, not 26.
- Believing that order doesn't matter in subtraction, as it doesn't in adding, so 8 - 15 seems the same as 15 - 8.
The lesson shows every step, so your child sees why it works. Read our parent's guide to explaining why subtraction strategies work →
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More 2nd grade Numbers & Place Value, with questions your child answers along the way.
Questions parents ask
Does my child need an account to watch?
No. You can watch this on any device at any time. If your child would like to practice explaining why subtraction strategies work, and you'd like parent-friendly reports on your child's progress and growth, you can join Bobby's Math Club for unlimited free practice.
What happens when my child answers a question?
A right answer gets a cheer, and the lesson carries on. If your child isn't sure, they can tap "I don't know yet", and Bobby gives the answer and shows another example. Nothing is scored or stored.
Is this the same lesson that's on YouTube?
Yes. Here, the lesson stops at each question and waits for your child to answer. On YouTube, each question stays on screen for a few seconds, and then the lesson plays on.
Where can I learn more?
There's a short, kid-friendly lesson like this one for every Pre-K to 5th grade math skill, all in our video library. Our parent's guide to explaining why subtraction strategies work has more on where kids get stuck and how you can help at home. In the club, your child practices at just the right level, about five minutes a day, and you get parent-friendly reports as they grow. Learn more about how it works →
Practice explaining why subtraction strategies work
Questions at your child's level, about five minutes a day, on explaining why subtraction strategies work and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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