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### Course: MAP Recommended Practice>Unit 14

Lesson 25: Multiply by tens word problems

# 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.
• 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.
• 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.
• this is hurting my brain
• 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?
• 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.
• but how this isn't the correct process like this the answer would 100 percent be different
• ahh i love math
• me too
• why cant we just multiply 5x7 and add a 0 to the end
(1 vote)
• You can! And that's exactly what Sal is saying in the video. For example, for the second question, at :

` 50 × 7`

2. Remove the zero from 50 by splitting it up into 10×5.
` 50 × 7 = 10 × 5 × 7`

3. Now you can multiply (5×7) to get 35, as you suggested.
` 10 × (5 × 7) = 10 × 35`

4. Finally, you add the zero to the end, which is the same as multiplying by 10.
` 10 × 35 = 350`