Multiplying fractions by whole numbers on a number line

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Maths5th grade math1:512 check-ins

About this video

Sal uses a number line to multiply whole numbers by fractions. He jumps by the fraction again and again: five jumps of 1/3 land on 5/3, two jumps of 4/3 land on 8/3, and three jumps of 3/2 land on 9/2.

You'll be able to

  • show a whole number times a fraction as repeated jumps on a number line.
  • multiply a whole number by a fraction by multiplying the numerator.

Key words

number line
A line with numbers in order that you can jump along.
numerator
The top number of a fraction, telling how many parts you have.
Transcript

We're asked to move the orange dot to the number that equals five times 1/3. Alright, so one way to think about it, we just have to move 1/3 five times. So let's do it once, so that's going to be 1/3, you do it twice, you get to 2/3, you do it three times, you get to 3/3, four times, you get to 4/3, five times, you get to 5/3.

Five times 1/3 is gonna be 5/3. Or you could say five 1/3, which is the same thing as 5/3, hopefully that makes some sense. Let's do some more examples here. So let's say we need to figure out, so let's see, it says move the orange dot to the number that equals two times 4/3.

Alright, so one times 4/3 is just gonna get us to 4/3, and then if we have another 4/3, we're gonna add 4/3 to that, so we're gonna move another 4/3 to the right. So 4/3 plus 4/3 would get us to 8/3. 8/3, I'm having trouble moving this, 8/3. So one times 4/3 is just 4/3, and then two times 4/3 is 8/3.

And notice that's the same thing as two times four, which is eight, over three, 8/3. Let's do one more of these. So, move the orange dot to the number that equals three times 3/2. So this is gonna be 0/2, that's just zero, so you could do that a zero times 3/2.

One times 3/2, well that will just get us to 3/2. Two times 3/2, we'll add another 3/2, so that'll get us to 6/2. And then three times 3/2, we'll add another 3/2, that gets us to 9/2, and we're done.

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