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5 January, 02:21

A project will take Mr A and Mr B 12 days to complete. Now that both of them work for 4 days, with the rest to be completed by Mr A in 10 days, find the number of days Mr B take to complete this project by himself.

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  1. 5 January, 02:48
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    Answer: 5 days

    Step-by-step explanation:

    If a project will take Mr A and Mr B 12 days to complete, this means that

    1/A + 1/B = 1/12

    (A+B) / AB = 1/12

    AB / (A+B) = 12

    Cross multiply

    AB = 12A + 12B ... (1)

    Now that both of them work for 4 days. Part of the job completed is

    AB / (A+B) = 4

    AB = 4A + 4B ... (2)

    Minus equation 2 from 1

    8A + 8B = 0 ... (3)

    The remaining day = 8 days

    If Mr A can complete this in 10 days,

    The number of days Mr B take to complete this project will be

    1/10 + 1/B = 1/8

    1/B = 1/8 - 1/10

    1/B = (10 + 8) / 80

    B = 80/18

    B = 4.444 days

    Approximately 5 days
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