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# Multiplying fractions word problem: laundry

Sal solves a word problem by multiplying 2 fractions. Created by Sal Khan.

## Want to join the conversation?

• 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".
• Sal chose the fourth option but, as they said how much detergent will be left, we can to choose the first option because it makes more sense. Why did sal choose the fourth option instead of the first one??
• In the first option, they're saying 2/3 MINUS 1/2. We are trying to find the answer for 2/3 TIMES 1/2. Hope this helps.
• how do you simplfy
• Simple. For example, 2/4 = 1/2 because you halve the numerator and the denominator to the simplest fraction possible.
(1 vote)
• I guess I'm still confused as to when the problem requires multiply and when it requires divide.
• . .
U
• The book had 27 pages. (Jimmy read 4 pages on Monday, 9 pages on Tuesday and there were 14 more pages to go.🤔
• 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 vote)
• 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.
• Isn’t it meant to halve it? How is 1/3 if you multiply 1/2 of 2/3? I still don’t get it
(1 vote)

## Video transcript

Gina had 2/3 cups of laundry detergent. She used half of the detergent on Friday to wash all of her sheets. How much detergent does she have left? So we're essentially going to take half of 2/3, or 1/2 times 2/3. So let's see which of these choices match up. So we should be taking 1/2 times 2/3. Well, here they're taking 2/3 minus 1/2, so this isn't going to be right. Here they're going to be taking-- let's see, 1/3, because 2/3 times 1/2, this is exactly what we want to do. We want to take half of 2/3. And we multiply the numerators, 2 times 1 is 2. Multiply the denominators, 3 times 2 is 6. You have 2/6. You could say the 2/6 has either been used up or 2/6 is left. And 2/6 is the exact same thing as 1/3. Divide the numerator and the denominator by 2, so this looks right. And so here 1/6 cup, well, we know it's not 1/6 cup. We know it's 1/3 cup. So here, 1/3 cup, because 2/3 is equal to 1/3 plus 1/3, that's right. So half of 2/3 must be 1/3. This is exactly right as well. These are both completely reasonable ways to getting to the right answer that Gina has 1/3-- she used 1/3 of a cup of laundry detergent, and she has 1/3 left.