WEBVTT

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將7/8寫成小數及百分數

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我們會從小數開始，然後我們會發現

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其實把小數化為百分數還滿容易的

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現在，不論何時你看到這樣的問題

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其實有時還滿令人困惑的

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這就像，我如何把它變成小數，

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或一個分母為100的分數，或一個百分數?

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你總是要記得7/8

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是等同於…

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.

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等同於7除以8

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不是8除以7

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7除以8

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分子除以分母

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好，那我如何將它變為小數呢?

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我們其實就是做一個長除法問題

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但我們即使到小數點後面還要繼續除，也就是我們

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不會有餘數，或者要直到數字開始不斷重覆

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你會了解我們在說什麼

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在這題，我們不會有一直重覆的數字

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讓我們來試試吧

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所以，它是7除以8

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.

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所以8除7是多少?

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好，8沒辦法乘以整數接近7

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商數是0

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事實上，我們因此確定是正確的

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讓我們寫上小數點

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你可以視這為8除7.000

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你可以在後面不斷加上0，直到

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你除盡為止

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所以我們有小數點在這邊，在7的後面

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在上面這邊

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所以，8除7等於0乘以

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0乘以8等於0

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減掉

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7減0等於7

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現在把0放下來

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把一個0放下來

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變為70

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8除70是多少?

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8x8=64，這樣行得通

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8x9=72

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太大了

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所以就是8

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.

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8x8=64

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減掉，70-64=6

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你還是有餘數，所以繼續

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把另一個0放下來

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所以你把另一個0放下來

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然後，8除60是多少

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8x8=64，太大了

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8x7=56，這行得通

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所以就是7

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7x8=56

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減掉

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60-56=4

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我們還是有餘數，讓我們繼續

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把0放下來

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所以，讓我們把0放下來

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8除40是多少?

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好，8x5=40，這剛剛好

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所以就是5

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5x8=40

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減掉

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沒有餘數

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所以關於小數，我們剛算出來7/8

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等於7除以8，就等於0.875

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所以7/8寫成小數是0.875

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現在我們做完了小數的部分

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下一個是要做百分數

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如果你已經有小數了，要做百分數就

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很容易

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你只要將小數點往右移兩位

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然後放一個百分比符號

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我想為什麼這行得通是很合理的

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現在你會說，每100有多少?

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你可以把這視為千分之875

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讓我把這寫下來

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你可以將這視為分數

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你可以說，好，這等於875/1000

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這是我們以前學的。這是

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千分位

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或者你可以將它寫做87.5/100

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如果你只移小數點兩位，它是87.5/100

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或者如果你只有這個，然後把分子、分母同除以10

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你會得到這個

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這基本上就是每100有87.5，所以

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第二個答案在這邊，這就是說每100有87.5

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或者百分比

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所以這就等於87.5%

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所以這給了你為什麼行得通的理由

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但真的簡單的方式，如果你有小數要變為百分數

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你把它乘以100

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然後放一個%在後面，基本上就是除以100

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所以你乘以又除以

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100

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如果你將這乘以100，就等於

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把小數點往右移兩位

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就變為87.5

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然後你想要放上%

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這會變為百分之…

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所以你乘以100，然後又除以100

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你並沒有改變這個數字

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希望，你能理解這道理

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另一個記憶的方式，因為有時你可能會困惑

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我要把小數點往右嗎?

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還是往左? 小數點的數字

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總是會比百分數的數字部分

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來得小

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不但比較小，而且

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剛好會差100倍

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剛好會比87.5

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小100倍

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很明顯地，當你寫下%，這些就會變成

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一樣大

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.