Explain why adding by tens and ones works
Being able to say why a method works gives your child the confidence to use it with new numbers and to notice if something has gone wrong. If your child only follows steps, they can get stuck if a problem looks a little different. Knowing the reason lets them adjust. This habit of reasoning carries into every later grade, from multiplying in 3rd grade to fractions in 4th and 5th.
In this video, your child will learn to explain how we add tens and ones.
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
34 + 23 = ?
Example 2
46 + 35 = ?
Your child's turn
57 + 26 = ?
The three key steps
- 1Numbers are tens and ones.
- 2Tens with tens, ones with ones.
- 310 ones make 1 new ten.
Mistakes to listen for
- Describing the steps but not the reason, saying "I carried the one" without knowing that the one stands for a ten.
- Using a drawing that doesn't match the numbers, such as drawing 36 as 6 tens and 3 ones.
- Working out 9 + 27 all over again after finding 27 + 9, rather than explaining that order doesn't change a sum.
The lesson shows every step, so your child sees why it works. Read our parent's guide to explaining why addition 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 addition 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 addition 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 addition strategies work
Questions at your child's level, about five minutes a day, on explaining why addition strategies work and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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