math

posted by clive

A and B can do a piece of work in 12 days. They started to work together but A left after a few days. If B alone worked for 20 days, the whole work was finished in 24 days. How long would A take to complete the work???

question is really confusing :/

  1. Steve

    1/a + 1/b = 1/12

    So, if A left after n days, A&B did n/12 of the work.

    20/b = 1 - n/12
    240 = 12b - nb
    b = 240/(12-n)

    so,
    1/a + (12-n)/240 = 1/12
    240 + (12-n)a = 20a
    a = 240/(8+n)

    I agree the question is confusing. The exact conditions seem ambiguous.

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