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## 6th grade (Illustrative Mathematics)

### Unit 3: Lesson 8

Lesson 15: Finding this percent of that# Percent of a whole number

There are several different ways to solve problems involving percentages, decimals, and fractions. Watch as Sal finds the percentage of a whole number. Created by Sal Khan.

## Want to join the conversation?

- at a scale of 500 percent a measurment is 165mm. what is the actual size?(7 votes)
- The video teaches how to find a percentage of a number, here you're given the percentage and looking for the original number, so you should reverse the operation, and do division.

What is the number when multiplied by 500/100 (that's 500%) gives 165?

? x 500/100 = 165

You can divide 165 by 500/100 to find the answer, or since we're dividing by a fraction, you can just multiply by its reverse, so it becomes likes this:

165 x 100/500 = ?

(165 x 100) / 500 = 16500 / 500

16500 / 500 = 33

The original number should be 33.(10 votes)

- At0:55, how do you turn the improper fraction into a mixed number?(4 votes)
- You can just divide the numerator by the denominator(2 votes)

- I don't understand how Sal turned the fraction into a decimal. How is 4/5 related to 4 divided by 5? (At1:00)(0 votes)
- The slash in between the 4 and the 5 means division. All fractions are division sentences written in a different form. To convert a fraction to a decimal, you divide the numerator by the denominator. For 4/5, you divide 4 by 5 to get 0.8(16 votes)

- These comments are very old!

Not to waste your time reading this, but if i did waste your time I'm so sorry(7 votes)- then stop doing it(1 vote)

- The video teaches how to find a percentage of a number, here you're given the percentage and looking for the original number, so you should reverse the operation, and do division.

What is the number when multiplied by 500/100 (that's 500%) gives 165?

? x 500/100 = 165

You can divide 165 by 500/100 to find the answer, or since we're dividing by a fraction, you can just multiply by its reverse, so it becomes likes this:

165 x 100/500 = ?

165 x 100 = 16500

16500 / 500 = 33

The original number should be 33.

It will help you to understand...if you could then hit a like 👍🏻👍🏻(7 votes) - this is too quick can someone explain it to me?(2 votes)
- So basically 50% of 100 is 50, and 50% of 5 is 2.5, if you get fractions and decimals then this is easy.

Here is a method to make calculating percentages easier.**Graph paper or any paper recommended**

Let's say I want to find 80% of 200, then I would write 200 x 80 (over 100)= ?. The two 0s from the 80 over 100 and 200 cancel out each other. 80 * 2= 160, so 160 is 80% of 200.

Hope this helps(10 votes)

- Can you explain it better Sal other then that Khan Academy is awsome(3 votes)
- Multiply the whole number by 100. The resulting answer is its value as a percentage. Another way is to add a decimal point after the whole number such as 4, and then move the decimal two spaces to the right, fill in each of those empty spaces with a zero, and add a percentage symbol = 400%.(3 votes)

- At0:17, how does multiplying 30/100 (or 3/10) by 6 (or 6/1,) equal 30% of 6?

Or 0.3 (or 0.30) by 6 equal 30% of 6?(3 votes)- Pay attention to the whole video or try the arithmetic course and see if that helps.(3 votes)

- how do you work out 17 out of 30 as a percent(4 votes)
- i dont know sorry(0 votes)

- what if it doesn't end in an improper fraction then we can't divide the denominator into the numerator I am really confused right now and I thought I was good at this stuff :( and what is 284 % of 400?(4 votes)
- 284% of 400 is equal to 284/100 * 400. You simplify and then get 284*4 (divided 400 by 100 and got 4) which is equal to 1136.(3 votes)

## Video transcript

Let's see if we can figure
out what 30% of 6 is. So one way of thinking
about 30%-- this literally means 30 per 100. So you could view
this as 30/100 times 6 is the same thing as 30% of 6. Or you could view this
as 30 hundredths times 6, so 0.30 times 6. Now we could solve
both of these, and you'll see that we'll
get the same answer. If you do this multiplication
right over here, 30/100-- and you
could view this times 6/1-- this is equal to 180/100. And let's see. We can simplify. We can divide the numerator
and the denominator by 10. And then we can divide the
numerator and the denominator by 2. And we will get 9/5, which is
the same thing as 1 and 4/5. And then if we wanted to write
this as a decimal, 4/5 is 0.8. And if you want to
verify that, you could verify that
5 goes into 4-- and there's going
to be a decimal. So let's throw some
decimals in there. It goes into 4 zero times. So we don't have to
worry about that. It goes into 40 eight times. 8 times 5 is 40. Subtract. You have no remainder, and
you just have 0's left here. So 4/5 is 0.8. You've got the 1 there. This is the same
thing as 1.8, which you would have gotten
if you divided 5 into 9. You would've gotten 1.8. So 30% of 6 is equal to 1.8. And we can verify it
doing this way as well. So if we were to multiply
0.30 times 6-- let's do that. And I could just write that
literally as 0.3 times 6. Well, 3 times 6 is 18. I have only one digit
behind the decimal amongst both of these
numbers that I'm multiplying. I only have the 3 to the
right of the decimal. So I'm only going
to have one number to the right of
the decimal here. So I just count one number. It's going to be 1.8. So either way you think about
it or calculate it, 30% of 6 is 1.8.