一條難度十分高的英文百分數題

Peter claims that when a number x is increased by 10% and then decreased by 10%, the value of x is unchanged.

His calculation: x(1 + 10% - 10%) = x

Peter os wrong. Point out the mistake.

5 個解答

評分
  • 1 十年前
    最愛解答

    The equation should be

    X (1+10%) (1-10%) = X

    The question means increment by 10% is X (1+10%) <= New amount

    Then the increased amount decrease by 10%, i.e. the new amount times (1-10%)

    So, it should be X (110%) (90%) =X

    Then, 99% X = X

    X seems equal to "0"

  • 1 十年前

    Peter's calculation is wrong. The right method is as follows:

    new value of X = (1+10%) (1-10%) X

    = (1.1) (0.9) X

    = 0.99X

    Therefore, new value of X should become less.

    資料來源: myself
  • 1 十年前

    x is increased by 10% ------>(1+10%)x = 1.1x

    then decreased by 10%----> (1-10%)* 1.1x

    ----->0.99x

  • Thomas
    Lv 6
    1 十年前

    When a number x is increased by 10%, it becomes 1.1x

    And then decreased by 10%, it becomes 0.99x

    The value of x has been decreased by 1%

    His mistake is that the formula should be

    x (1+10%)(1-10%) instead of x(1 + 10% - 10%)

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  • 1 十年前

    100% + 10% = 110%

    110% * 0.9 = 99%

    X went down from 100% to 99%

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