If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# 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.
• why didn't you just multiply the thing then just working it out the long long long way!?
• Well, he is just doing this because it is gonna give you a better comprehension if he does a harder problem. I mean, if he did 1*7 (1x7 or 1 times 7), you would not learn anything because you already know the answer, and it won´t help you at all.
• why cant we just multiply 5x7 then add a 0 to the end?
• you can but he does it so it will be clear to the watchers (what I mean is that it is people watching)
(1 vote)
• 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.
• why 4x9 really hard? i dont undrstand this thing. if someon can help me pls help
• 4 x 9 = 36. Multiplication is repeated addition. If you have problems multiplying a number, try adding that number to itself. For example, for 4 x 9, you could either add 4 + 4 = 8 + 4 = 12 + 4 = 16 + 4 = 20 + 4 = 24 + 4 = 28 + 4 = 32 + 4 = 36 or 9 + 9 = 18 + 9 = 27 + 9 = 36. Another strategy would have been multiplying and then subtracting: 4 x 10 = 40 - 4 = 36.
• keyanna is right why can`t we do that
• Can we say that 50x7 is (1/2 (=one half) times 100) x 7 what is the same thing as half times 700? We'd still get 350, what is the right answer here.
• Yes, both ways work.
If you want to use 100×7 to calculate 50×7, all you need to do is add a "times one-half" somewhere in the expression (since 50 is half of 100).
So,
100×7 × 1/2 = 700 × 1/2 which is equal to 350.

If you were to just calculate 50×7 as-is, you'd also get 350 (35 with a zero added on).

• not always for example 50&50
• i put this all on my note book thank khan
• All you had to do was multiply 50 x 7 right? You see the number 5 and 7 and you'll think that oh! I think we need to multiply 5 x 7 and get the answer of 35! And then i will add my zero in and get my answer of "350".
See? Ez math.