Multiply by tens
This is the bridge your child crosses between knowing times facts and multiplying bigger numbers. In 4th grade, your child will find 4 x 73 by adding 4 x 70 and 4 x 3, and work out 30 x 40 with the same reasoning. Understanding tens, rather than a rule about adding a zero, also keeps things working when decimals arrive in 5th grade.
In this video, your child will learn to multiply by multiples of ten.
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
3 × 40 = ?
Example 2
6 × 50 = ?
Your child's turn
9 × 80 = ?
The three key steps
- 1Write it as tens.
- 2Use a times fact on the tens.
- 3Ten tens make a hundred.
Mistakes to listen for
- Multiplying the digits and forgetting the tens, writing 4 x 70 = 28 instead of 280.
- Writing the wrong number of zeros when the fact already ends in zero, so 5 x 80 becomes 40 or 4,000 instead of 400.
- Using the add-a-zero trick without knowing why, so they cannot tell whether 3 x 60 = 180 is reasonable.
The lesson shows every step, so your child sees why it works. Read our parent's guide to multiplying by tens, like 4 x 70 →
Is your child ready to practice what they've learned?
Bobby's Math Club offers unlimited practice for free.
Join the clubMore kid-friendly lessons
More 3rd 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 multiplying by tens, like 4 x 70, 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 multiplying by tens, like 4 x 70 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 multiplying by tens, like 4 x 70
Questions at your child's level, about five minutes a day, on multiplying by tens, like 4 x 70 and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
Join the club