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匿名 發問於 科學及數學數學 · 1 十年 前

1條數學題

Mr.Lee takes 8days to finish a job. If Mr. Chan works alone, he needs 18days more than they work together.Find the time taken for Mr.Chan to finish the job alone.

3 個解答

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  • 1 十年 前
    最佳解答

    Let x days be the time that they work together to accomplish the job.

    Therefore, Mr. Chan takes x + 18 days to finish the job.

    x[1/8 + 1/(x + 18)] = 1

    x[(x + 18 + 8)/8(x + 18)] = 1

    x(x + 26) = 8(x + 18)

    x^2 + 26x = 8x + 144

    x^2 + 18x - 144 = 0

    (x + 24)(x - 6) = 0

    x = 6 or -24 (rejected)

    So, no. of days for Mr. Chan to do the work alone

    = 6 + 18

    = 24 days

    資料來源: Myself~~~
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  • 1 十年 前

    中文的解釋是what?

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  • 1 十年 前

    let x be time taken for Mr.Chan to finish the job alone

    x - 18 = 1/(1/x + 1/8)

    x - 18 = 8x / (x + 8)

    (x - 18)(x + 8) = 8x

    x^2 - 18x - 144 = 0

    (x - 24)(x + 6) = 0

    x = 24 or x = -6 (rejected)

    Mr.Chan takes 24 days to finish the job alone

    2007-10-01 14:18:44 補充:

    oh! 慢左, 不過我好似簡單 d 喎,多多支持我,我要升級..唔該

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