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  • - [Instructor] So they are telling us that

  • r fifths is equal to eight tenths

  • and we need to figure out what is r going to be equal to

  • and they help us out with this number line

  • where they've put eight tenths on the number line.

  • That makes sense because to go from zero to one,

  • they've split it into one, two, three, four,

  • five, six, seven, eight, nine, ten equal jumps

  • and at this point, we have gone eight of those ten

  • equal jumps between zero and one so that is eight tenths

  • and they've also labeled one fifth for us

  • and one way to think about it is

  • if we look at these bold lines,

  • zero,

  • one,

  • two,

  • three,

  • four,

  • five,

  • if you just look at the purple, we have five equal jumps.

  • So each of those jumps are a fifth

  • and so it makes sense that our first jump

  • right over here gets us to one fifth

  • and you can see that

  • that is equivalent to two of the tenths.

  • I'll just write that up here so we can see that equivalence.

  • One fifth is equal to two tenths

  • but how many fifths is equal to eight tenths?

  • Pause this video and try to figure it out.

  • All right, well this is one fifth.

  • If we do one more jump of a fifth, that would be two fifths.

  • Then if we go another fifth,

  • that will get us to three fifths

  • and then if we go another fifth,

  • that will get us to four fifths

  • which we see is exactly equivalent to eight tenths

  • and that makes sense because we also saw that

  • every fifth is equivalent to two tenths.

  • So four fifths is going to be equivalent

  • to eight of those tenths.

  • We see that very clearly right over here

  • and so r is equal to four.

  • Four fifths is equal to eight tenths.

  • So r is equal to four.

  • Let's do another example.

  • What fraction is equivalent to point A?

  • So pause this video and see if you can figure that out.

  • All right, so let's figure out where point A is.

  • So to go from zero to one,

  • we have one, two, three, four, five, six equal jumps.

  • So each of these jumps are a sixth.

  • So going from zero, one jump will get us to one sixth,

  • then two sixths, then three sixths,

  • then four sixths, then five sixths

  • and so can we see four sixths in the choices?

  • No I do not see four sixths.

  • So we have to find an equivalent fraction to four sixths.

  • So we could go choice by choice.

  • The first choice has five sixths.

  • Well we very clearly see that five sixths

  • would be here on the number line

  • which is clearly a different place than four sixths.

  • So we could rule out this first choice

  • but what about these other ones?

  • Let's see, let's see how we can think about.

  • Four fifths versus four sixths.

  • Could those be equivalent?

  • If I have four out of five versus four out of six,

  • that's not feeling too good

  • so I'm gonna put like a curly line through it.

  • That's not feeling right, that if I could have

  • four out of five equal jumps or five equal sections,

  • that that would be the same

  • as four out of six equal sections.

  • If I divided it into six equal sections,

  • each of those sections are going to be a little bit

  • smaller than if I divided into five equal sections.

  • So if I have four of each,

  • they're going to be a different value.

  • Actually when I talk it out like that,

  • I feel even more confident that I could rule this one out.

  • Now what about six fourths?

  • Well one way to think about it

  • is four fourths would be equal to one.

  • So six fourths is going to be beyond one.

  • So it's definitely not going to be where A is,

  • so I could rule that one out

  • and we could say oh, well maybe it's just going to be D

  • but let's make sure that this makes sense.

  • Two thirds, what does two thirds look like?

  • Well let me try to divide this part of the number line

  • from zero to one into thirds, into three equal sections.

  • So I have zero there

  • and then that could be one third,

  • two thirds and then three thirds.

  • That looks like three equal sections.

  • So this is one third,

  • this is two thirds, I'm making another jump of a third

  • and then when I get to one, of course that is three thirds

  • or we could have said six sixths

  • and so point A,

  • which is right over here I'm writing over it,

  • that is indeed equal to two thirds.

  • You can see each jump of a third is equal to two sixths.

  • So it makes sense that four sixths is equal to two thirds

  • or that two thirds is equal to four sixths

  • so I like this one.

- [Instructor] So they are telling us that

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A1 初級

數字線上的等分 (Equivalent fractions on number lines)

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    林宜悉 發佈於 2021 年 01 月 14 日
影片單字