Yiu Man asked in 教育及參考書教學 · 1 decade ago

有關%的數

Q1: 100 / 100 * 50% = 2 why?

如果先計算 100/100 = 1, 咁 1 * 50% = 0.5

明明先 * / 後 + -, 點解有%不能先除?

Q2: 某公司在報價單上mark up 15%, 如產品成本$100, 點解算式會是 $100 / 0.85 而不是 $100(1+15%)?

1 Answer

Rating
  • 1 decade ago
    Favorite Answer

    我唔係好明你第2條問乜,所以我只係答你第1題啦

    第一題既5%,即係0.5啦,咁即係

    100/100x0.5

    正常做法就係將分母個100乘左0.5先,即係100x0.5=50

    =100/50

    =2

    所以答案係2

    又或者你可以改變個分母(擴分),由於而加分母乘左0.5

    所以你可以除番0.5,不過同時你個分子都要除番0.5

    100÷0.5/100x0.5÷0.5

    =200/100

    =2

    所以答案都係2

    至於點解唔係100÷100x0.5=0.5

    係因為個0.5唔係乘個分子,而係乘個分母

    俾你睇明d應該係咁100/(100x0.5)=2

    你計到個0.5答案係因為你將條式整成咁

    (100/100)x0.5

    所以會等於0.5,咁就錯左喇

    睇住下面,呢個係正確做法:

    100 100

    ---------- = ---------- = 2

    100x0.5 50

    至於你錯係因為咁:

    100

    ----------x0.5 = 1x0.5 = 0.5

    100

    從而講多一次,因為個x50%係係個分線下面,

    即係要黎乘個分母,唔係乘個分子

    所以答案係2

    等我做埋擴分果個俾你睇啦(分子分母都乘或者除一樣野係無問題):

    100 100÷0.5 200

    ---------- = ---------------- = ---------- = 2

    100x0.5 100x0.5÷0.5 100

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