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## 5th grade

### Course: 5th grade > Unit 6

Lesson 6: Multiplying fractions word problems# Multiplying fractions word problem: laundry

CCSS.Math:

Sal solves a word problem by multiplying 2 fractions. 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(4 votes)
- 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.(8 votes)

- i have no upvots(5 votes)
- Why do you teach negative fractions to little kids in 5th grade(2 votes)
- To some students, they will be ready to take pre-algebra in sixth grade, therefore advancing to higher level math courses. Negative fraction is a foundation to future concepts that teachers would expect from high level classes.(6 votes)

- upvote me plz(4 votes)
- how do you simplfy(2 votes)
- Simple. For example, 2/4 = 1/2 because you halve the numerator and the denominator to the simplest fraction possible.(2 votes)

- 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??(2 votes)
- 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.(2 votes)

- Why multiply? Shouldn't he subtract? To get what's left he should subtract.(1 vote)
- 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".(4 votes)

- Sal said, "She used a third of her detergent and has a third left". She actually used a 1/2

of her detergent.(0 votes)- 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.(4 votes)

- How do u know when a word problem is multiplying fractions or dividing fractions(3 votes)
- you do this and that you equal your head(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.