math

jon and jony can do a piece of work alone 12days and 24days respectively.they were working together but after a few days jon went away.then jony can do the
rest work in 3days.how many days are needed to complete the whole work?

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  1. jon does 1/12 per day

    jony does 1/24 per day

    together they do 1/12 + 1/24 = 1/8 per day

    it took jony 3 days to finish
    ... 3/24 = 1/8

    so together, they did 7/8 ... in 7 days

    7 + 3 = 10 days for completion

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