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  • - [Instructor] Let's say we wanna figure out

  • what eight divided by 4/10 is.

  • Pause this video and try to figure it out on your own

  • before we do it together.

  • All right, now one way to approach this is

  • to think about everything in terms of tenths.

  • And why tenths, you ask?

  • Well, I just described the second number as 4/10.

  • So what would eight be in terms of tenths?

  • Well, we know that one whole

  • is equal to 10/10,

  • so eight wholes is going to be equal to 80/10.

  • So I could write that down over here.

  • Instead of eight, I can write that as 80/10.

  • And I'm taking 80/10 and I'm dividing that by,

  • divided by 4/10.

  • I'm just writing out, 4/10.

  • So if I have 80 of something,

  • and if I'm diving it into groups of four of that something,

  • how many equal groups am I going to have?

  • Well, I'm gonna have 80 divided by four groups,

  • or 80 divided by four, eight divided by four.

  • Actually, let me just write that down.

  • This is going to be equal to 80 over four

  • or 80 divided by four.

  • And eight divided by four is two,

  • so 80 divided by four is going to be equal to 20.

  • So eight divided by 4/10 is equal to 20.

  • Another way that you could think about that is

  • to rewrite eight divided by 4/10

  • as eight over 4/10.

  • Over 4/10.

  • And then if you wanted to rewrite this,

  • you could say, "Hey, can I multiply the numerator

  • "and the denominator by some quantity that'll get rid

  • "of the decimal in the denominator?"

  • Well, I could multiply the denominator by 10.

  • And if I don't wanna change the value of the fraction,

  • I have to multiply the numerator by that same amount.

  • Well, what does that get us?

  • Well, this is going to be equal to,

  • in the denominator right over here,

  • I'm just going to have a four.

  • So we got rid of the decimal.

  • In the numerator, I am going to get 80.

  • So once again, we get 80 over four, which is equal to 20.

  • Let's do another example,

  • but in this case we'll deal with hundredths.

  • So let's say we want to figure out

  • what is 48

  • divided by 0.24

  • or 24/100?

  • Pause this video and try to figure that out.

  • All right, well, we can do something very similar.

  • This time we're dealing with hundredths,

  • so we could try to express everything

  • in terms of hundredths.

  • So 48 is equal to how many hundredths?

  • Well, we know that one is equal to 100/100,

  • so 48 is going to be equal

  • to 48 times 100/100.

  • Maybe I'll just write it like that.

  • Or you might be able to say, "Hey, that's 4,800

  • "or 4,800/100."

  • So let's just, actually, I'll write it that way.

  • This is going to be 4,800/100

  • divided by, this is 24/100.

  • 24/100.

  • And so what's that going to be?

  • Well, same logic as we used up here.

  • If I have 4,800 of something or 4,800 of something

  • and if I'm dividing it into equal groups

  • of 24 of that something,

  • well, I'm going to have 4,800 divided by 24 equal groups.

  • So this is going to be equal to 4,800

  • over 24.

  • We could express 4,800 as, of course, 48 times a hundred.

  • So this is equal to 48

  • times 100 over 24.

  • And of course, you could view this as the same thing

  • as this is equal to 48 over 24.

  • 48 over 24, and many of you might have already done it

  • in your head, times 100.

  • What's 48 divided by 24?

  • Well, that is going to be equal to two.

  • So two times a hundred is equal to 200.

  • So this right over here is equal to 200.

  • You can also do it in this type

  • or do it similar to the way we did this

  • where instead of expressing it out as words,

  • you could express it as 48 over 24/100.

  • And instead of multiplying the numerator

  • and denominator by 10,

  • maybe you wanna multiply it by something else

  • to get whole numbers in both the numerator and denominator.

  • Think about that after this video,

  • and try to work it out that way as well.

- [Instructor] Let's say we wanna figure out

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A2 初級

整數除以小數的例子 (Dividing whole numbers by decimals examples)

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    林宜悉 發佈於 2021 年 01 月 14 日
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