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  • - [Instructor] You are likely already familiar

  • with the relationship between multiplication and division.

  • For example, we know that three times six

  • is equal to 18.

  • But another way to express that same relationship

  • is to say, all right, if three times six is 18,

  • then if I were to start with 18 and divide it by three,

  • that would be equal to six.

  • Or you could say something like this,

  • that 18 divided by,

  • divided by six

  • is equal to three.

  • Now we're just going to extend this same relationship

  • between multiplication and division

  • to expressions that deal with fractions.

  • So for example,

  • if I were to tell you that 1/4 divided by,

  • and I'm going to color-code it, divided by two

  • is equal to 1/8,

  • is equal to 1/8,

  • how could we express this relationship,

  • but using multiplication?

  • Well, if 1/4 divided by two is equal to 1/8,

  • that means that 1/8 times two is equal to 1/4.

  • Let me write this down, or I could write it like this.

  • I could write that 1/4 is going to be equal to,

  • is going to be equal to 1/8 times two,

  • times two.

  • And we could do another example.

  • Let's say that I were to walk up to you on the street

  • and I were to tell you that, hey, you, 42

  • is equal to

  • seven,

  • seven divided by 1/6.

  • In the future, we will learn to compute things like this.

  • But just based on what you see here,

  • how could we express this same relationship

  • between 42, seven, and 1/6,

  • but express it with multiplication?

  • Pause this video, and think about that.

  • Well, if 42 is equal to seven divided by 1/6,

  • that means that 42 times 1/6

  • is equal to seven.

  • Let me write that down.

  • This is the same relationship as saying that 42 times

  • 1/6,

  • 1/6 is equal

  • to seven.

  • Now let's say I walk up to you on the street

  • and I were to say, all right, you,

  • I'm telling you that 1/4 divided by,

  • divided by six

  • is equal to some number

  • that we will express as t.

  • So can we rewrite this relationship between 1/4, six, and t,

  • but instead of using division, use multiplication?

  • Pause this video, and try to think about it.

  • So if 1/4 divided by six is equal to t,

  • based on all of the examples we've just seen,

  • that means that if we were to take t times six,

  • we would get 1/4.

  • So we could write it this way, t times six,

  • times six is going to be equal to 1/4.

  • If this isn't making sense,

  • I really want you to think about how this relationship

  • is really just the same relationship we saw up here.

  • The only new thing here is

  • instead of always having whole numbers,

  • we're having fractions

  • and representing some of the numbers with letters.

- [Instructor] You are likely already familiar

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A2 初級

分数の掛け算と割り算の関係 (Multiplication and division relationship for fractions)

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    林宜悉 に公開 2021 年 01 月 14 日
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