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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.

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• 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.
• 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".
• How do u know when a word problem is multiplying fractions or dividing fractions
• 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.
• 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.
• 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)
• Why didn't he just subtract I know it's a multiplication problem but it literally asked how much detergent she was left with.. after she used some that's just subtracting E.G "I had had 1 liter Cola or 4/4 of a cola I drank 2/4 how much is left I mean please someone explain logically thank a you.
• The truck is that she used half of the 2/3 that she had. If you subtract 1/2 from 2/3 you are assuming that she used a half of a full bottle's worth, not half of the 2/3.
When you multiply 1/2 x 2/3 you get 1/3, which is the actual amount Gina used. You can subtract 1/3 from 2/3 to get 1/3 which is the amount Gina has left. (Though that subtraction step sort of got glossed over in the video because we know that, being a half, the other half is going to be the same.)