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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.

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  • blobby green style avatar for user CecilieEpley5
    at a scale of 500 percent a measurment is 165mm. what is the actual size?
    (7 votes)
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    • duskpin ultimate style avatar for user Aria
      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)
  • aqualine ultimate style avatar for user Ryanne Mills
    At , how do you turn the improper fraction into a mixed number?
    (4 votes)
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  • winston default style avatar for user BS-732298
    I don't understand how Sal turned the fraction into a decimal. How is 4/5 related to 4 divided by 5? (At )
    (0 votes)
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    • stelly blue style avatar for user Hemm Anna
      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)
  • blobby green style avatar for user 28tmedina
    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)
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  • blobby green style avatar for user rashmi101083
    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)
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  • aqualine sapling style avatar for user georgie
    this is too quick can someone explain it to me?
    (2 votes)
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    • blobby blue style avatar for user Skylar
      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)
  • aqualine ultimate style avatar for user Stella
    Can you explain it better Sal other then that Khan Academy is awsome
    (3 votes)
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    • starky tree style avatar for user southside joji
      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)
  • piceratops tree style avatar for user Nabeel M.
    At , 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)
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  • blobby green style avatar for user Phelim Conway
    how do you work out 17 out of 30 as a percent
    (4 votes)
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  • aqualine ultimate style avatar for user angeletti45235
    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)
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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.