math

If one person can do a job in 60 minutes and another per can do it in 90 minutes, how long will it take them, working together, to do the job?

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asked by Kay
  1. first person does 1/60 job/min
    second does 1/90 job/min

    together they do
    1/60 + 1/90 = 3/180 + 2/180 = 5/180 job/min

    so
    (5/180)t = 1 job

    t = 180/5 = 36 minutes

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    posted by Damon

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