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Equivalent fraction and whole number multiplication problems

Sal relates mixed numbers to whole number/fraction multiplication problem. Created by Sal Khan.

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  • aqualine ultimate style avatar for user mothflight(Ivystar)
    can we do this in mixed fraction form too? and if we can how do we solve it?
    (13 votes)
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  • piceratops tree style avatar for user Evilredcat
    how would i multiply 1/4 by 96?
    or 1/4 of 96
    (7 votes)
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  • aqualine ultimate style avatar for user Pretty girl laya
    yuh get in to it
    (6 votes)
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  • purple pi purple style avatar for user Jen Gorman
    Why doesn't Khan ever say at the end something like " So it equals 8/3 which is also the same as 2 2/3"? Or in other word why doesn't he also mention the mixed number form of the answer?
    (6 votes)
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  • blobby green style avatar for user 28mshawver
    please answer. I will be checking in.
    (5 votes)
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  • blobby green style avatar for user Simon Caan
    Need help. 3 wholes 4/5 times ten
    (3 votes)
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  • aqualine ultimate style avatar for user Amara0960
    I don't really get the whole number times the fraction part.
    (6 votes)
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    • piceratops ultimate style avatar for user EmmaB
      Say you've got 15/12.
      There are fifteen 12ths, or fifteen 1/12ths.

      So 1/12 + 1/12 + 1/12... and you keep adding 1/12th onto each other 15 times until you get to 15/12.

      Remember 1/12 is just 1 piece of 12 total pieces divided, imagine it as a cake or pizza you've divided into 12 pieces and you count each piece.

      So you're only adding the Numerators (top numbers). the denominator (bottom number) never changes, so when you multiply a fraction by a whole number you're only multiplying the Numerator (top number).

      You can do it that way... but really the number you're multiplying with is also still a fraction it's 2 wholes so you can write it as 2/1 which is just another way to represent that it's 2 wholes, when you do this multiplying 1 fraction then becomes the same as multiplying 2 fractions cos you've now got 2 fractions.
      (0 votes)
  • hopper happy style avatar for user Mei Ling Frank
    why does he needs 3 groups of 4 1/3s?
    (5 votes)
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  • cacteye green style avatar for user Baymax
    What's a parenthesis? He said that in 1.44 - 1.54 from the video.
    (3 votes)
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    • piceratops ultimate style avatar for user Hecretary Bird
      A parenthesis is a symbol that looks like this: "(" or this: ")". If you have two parentheses, you can "section off" a part of your expression. In math, you're supposed to perform operations that are inside parentheses first, before you do anything else. For example, in 3 * (4 + 3), you would first add 4 + 3 and then multiply by 3.
      In the video, Sal deletes the parentheses because since the only operation in there is addition, you can do it in any order. Parentheses mainly come up when you have multiple operations in one expression, like in the right side of the second equation Sal writes.
      (4 votes)
  • winston baby style avatar for user JACOB YEAGER
    Why did you use the method that you did?
    (3 votes)
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Video transcript

So we have here, it says 2 times 4/3 is equal to 8 times blank. And what I encourage you to do is pause the video right now and try to think about what should go in this blank. So I'm assuming you've given your try. Now, let's think through this. So 2 times 4/3, we can literally view that as the same thing as-- if we rewrite the 4/3, this is the same thing as 2 times-- instead of writing 4/3 like this, I'm literally going to write it as four 1/3's. And I know it sounds like I just said the same thing over again. But I'm literally going to write 1/3 four times-- 1/3 plus 1/3 plus 1/3 plus 1/3. If you call each of these 1/3, you literally have four of them. This is four 1/3's. 2 times 4/3 is the same thing as 2 times, literally, four 1/3's. Now, what would this be? Well, this is going to be equal to-- let me just copy and paste this-- is going to be this two times. So copy, and then let me paste it. So that's one group of those 1/3's, of those four 1/3's, or one group of one of these four 1/3's. And then, we'll have another one. And then, we'll have another one. And we're going to add them together. That's literally 2 times 4/3. So let's add these together. Now what do we have? Well, we have a bunch of 1/3's. And we need to count them up. We have one, two, three, four, five, six , seven, eight 1/3's. This is literally equal to-- and we could, just to make it clear what I've just done, we could ignore the parentheses and just add up all of these things together. So that might make it a little bit clearer. So let me do that just to make it clear that I literally take-- I've taken eight 1/3's and I'm adding them together, which is the exact same thing as 8/3. So let me clear that, and let me clear that, let me clear that. And so this is literally, or this is clearly, or hopefully clearly, equal to 8 times 1/3. I have 8 1/3's there. So going back to the original question, what is this equal to? 2 times 4/3 is the same thing as 8 times 1/3. And we've already seen that 8 times 1/3, well, that's literally 8/3. So we could also write it like this-- 8 over 3. Let me do that 3 in that other color-- 8 over 3.