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Lesson 4: Multiplying by tens

# Multiplying by multiples of 10

Sal decomposes multiples of ten to multiply. Created by Sal Khan.

## Want to join the conversation?

• why cant we just multiply 5x7 then add a 0 to the end?
• for 50x7? You can. He's just explaining the underlying process here. With enough practice, you will be able to easily shift 0's around given a certain power of 10.
• How do you multiply 50x7
• The way in the video, we can do it by first multiplying `5 x 7` below:

``  5x 7——— 35``

Now, because `5 x 7 = 35` We have to account for the 0 on the 50, so all we do is add a zero to the end of our one digit by one digit multiplication answer. Which now turns 35 into 350, so now this is the picture:

``  50x  7———— 350``

So, we can now equate that `50 x 7 = 350`

Hope this helps!
• so we should just add a 0 when muitpliling by 10
• Yes your right also when multiplying by 100's 1000's etc. You just add the 0's to the number that you are multiplying by.
• so 50 x 7 is the same as 50 + 50 + 50 + 50 + 50 + 50 + 50?
• yes, the answer to 50 x 7 and 50 + 50 + 50 + 50 + 50 + 50 + 50 both equal 350.
• do we haft to watch this?
• For 60x7, can we just multiply 6x7 and then add a zero at the end?
• that's a good idea for numbers with only one zero. When a number has TWO zeroes (for example: 200 x 2), you should mulitply 2x2 and add TWO zeroes. Just so you won't get confused.
• you do good with multiple
• yes I do