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## 5th grade

### Course: 5th grade > Unit 7

Lesson 3: Dividing unit fractions by whole numbers# Dividing a unit fraction by a whole number

Sal uses a visual model to divide a unit fraction by a whole number.

## Want to join the conversation?

- Good video, but what is the non Common Core way to figure this out? What mathematical formula could be applied to solve this, sans drawing?(24 votes)
- Dividing by a whole number is the same as multiplying by its reciprocal. In this case, dividing by 5 is the same as multiplying by 1/5.
`1/3 ÷ 5`

is the same as`1/3 x 1/5`

*Multiply the denominators and numerators.*`1/3 ÷ 5 or 1/3 x 1/5 = 1/15`

(19 votes)

- Hi, I am working with my son to understand fraction division in terms of model. We kind of understand this model well, but when the lower fraction amount is divided by a bigger fraction, how do you model it ? for example 1/5 ÷ 1/2 ?(8 votes)
- draw a fraction diagram of five.Then you take 1/5 and divide it into a half.(7 votes)

- How would we interpret or understand 1/3 divided by 5?(7 votes)
- Basically you need to make the 5 a fraction, which is 5/1. Then you do 1/3*5 to get 1/15. Then do 1/15 / 1 to get 1/15. Then simplify (if needed, in this problem is not needed). Hope this helps! Please ask any further questions if you need it! :D(6 votes)

- Does 1/3 divided by 5 = 1/3 times 1/5(6 votes)
- You hit it there. You can just multiply with the periodic break, just as you can divide by the periodic break if you multiply (25 * 1/5 = 25 / 5)(6 votes)

- Im confused? what would be the answer for 1/5 diveded my 3 and 3 divided by 1/5?(2 votes)
- 1/5 divided by 3 can be rewritten as 1/5 times 1/3. To find the product of these, we can multiply the 1 from 1/5 to the 1 from 1/3, and multiply the 5 from 1/5 to the 3 from 1/3 to obtain the fraction 1/15.

Think about it like this: If 1/5 is being divided into 3 smaller parts, then its fraction is going to be 3 times smaller. Essentially the denominator is multiplied by 3.

For the second problem, 3 divided by 1/5 can be rewritten as 3 times 5. Multiply the two together to get your answer, 15.

Think about this one by visualizing 3 as a giant number and a 1/5 as a tiny number considering it's smaller than one. With this in mind, we know that our answer is going to be much larger than 3. Essentially, 3 times 5.

This may look a lot more complicated in the way I explained it, but that's only because I got into the nitty-gritty. It's mostly visualizing, for me at least.(12 votes)

- I don't understand what he's saying at "1:07" of the video(6 votes)
- Hello! What exactly is it you're having trouble with?(2 votes)

- First Sal shaded 1/3 and then, shaded 1/15, shouldn't it be 5/15?(6 votes)
- hey soo my thing is im am TRASHHHH at math. and I just needed a better understanding of this. so does anyone mind helping ... :)(4 votes)
- Why is it that when you divide the square into 5, you divide the entire thing, and not just the 1/3? Wouldn't that be (1/3 + 2/3)/5?(4 votes)
*you divide the entire square so you can find the correct amount of parts the whole is divided into. If you weren't to do this, you wouldn't get the correct denominator for your final answer, I struggled with this too; just keep trying! You'll get better.*:D(4 votes)

- All you could do is just in instead of doing that whole thing what you can do is just multiply the whole with the denominator and you get 1/15 because 3 X 5 = 15 and then just put 1 as the numerator.(4 votes)

## Video transcript

- [Instructor] So let's
see if we can figure out what 1/3 divided by five is. And I'll give you a hint. Try to draw out 1/3 of a whole and then divide it into
five equal sections. Pause this video and try to do that. I always try to work through it together and to help us as I promised
or I suggested I guess. We said let's draw 1/3. I will represent a whole by
that square right over there. And now let me split up
into three equal sections. So this is all hand drawn
with the aid of a computer. So it's not going to be perfect. But let's say that that
is three equal sections. It's roughly three equal sections. I didn't do it perfectly but you hopefully get the idea. And so 1/3 would be one of
those three equal sections. So that's a third right over there that I have just shaded in and I want to divide it into five. I want to divide it by five, I should say. So let's do that. So to divide it by five, I'm
gonna divide it into five equal sections. And if I'm dividing that one
into five equal sections, let me just divide all of the thirds into five equal sections. I'm essentially just going
to make five rows here. One, and I'm gonna eyeball it, so it's going to be approximate. Two, three, and then four
and five equal sections. I now split this whole into
one, two, three, four, five rows of equal height. Now if I go to my original
third and I divide it by five, I would be left with this right over here. But what fraction is this of the whole? Well what I've done now
is I've split my whole into 15 equal sections. How do I know that? Well I could count them. One, two, three, four,
five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15. Or you could just say look
I had one, two, three thirds and now each of those have been split into one, two, three, four,
five equal sections. So three times five is 15. So each of these is a 15th and so the 1/3 divided by five is just one of those 15ths. So that right over there
is one of those 15ths. So this is going to be equal to 1/15 and we are done.