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### Course: Arithmetic (all content)>Unit 5

Lesson 23: Multiplying fractions word problems

# Multiplying fractions word problem: laundry

Learn how to solve word problems involving multiplication of fractions. Watch examples of real-life scenarios where fractions are multiplied, and practice applying the concept to solve similar problems. Created by Sal Khan.

## Want to join the conversation?

• I don't think this is correct because 2/3 = 4/6 and 1/2 = 3/6 so 4/6 subtract 3/6 = 1/6
• Notice that Gina used half of the detergent, not half a cup of detergent.

She started with 2∕3 cup and used 1∕2 of it,
i.e. she used (1∕2)(2∕3) = 1∕3 cup.
Thereby she'd be left with 2∕3 − 1∕3 = 1∕3 cup.
• How do u know when a word problem is multiplying fractions or dividing fractions
• Why multiply? Shouldn't he subtract? To get what's left he should subtract.
• There are 2/3 cups of detergent and she uses 1/2 of it. She uses 1/2 of the detergent that she has, not 1/2 half of a cup. Usually, when you're trying to find a proportion of something, you're multiplying. The key word for multiplying is "of".
• So You Dont Divide The Denominator But You Divide The Numerator?
• Yes.

If we had divided only the denominator, It would make the value bigger (and as long as you have a positive- -fraction, it should be getting smaller!). So this would be incorrect.

If we divided both, it would be equal to the original value because that is the process of simplifying fractions. So this is also incorrect.

So now the only way that is left is for us to divide the numerator only. ( if you specifically want to know why, comment below!)
I hope this helps!

-Eun
• This isn't a homework question so can anyone figure out the answer to this question?
1/3 gallon milk poured into 5 equal sized cups. What fraction of a gallon of milk is in each cup.
• 1/15 gallons of milk is in each of the five cups, because 1/3 divided by 5 is equal to 1/15.
• How come in the video, they multiplied for some reason?? Shouldn't you subtract? That was confusing. Can someone explain the whole thing to me??
• Subtracting will do no good in this kind of problem. I can't really explain, but I can sense it... It seems rather obvious to me... Although, ( I don't want to offend anybody, side note), some people might be oblivious to that.
(1 vote)
• Sal said, "She used a third of her detergent and has a third left". She actually used a 1/2
of her detergent.
• Sal said she used a third CUP of her detergent, which is equal to a half of her detergent before she used it.

As in, a half of 2/3 cups is 1/3 cup.