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A contractor finds that it takes a crew A 6 hours to construct a wall of a certain size. Crew B takes 8 hours to construct a wall of the same size. How long will it take if they work together?

  • algebra -

    rate of A crew = wall/6
    rate of B crew = wall/8
    combined rate = wall/6 + wall/8
    = 7wall/24

    time with combined rate = wall/(7wall/24)
    = 24/7
    = 3.428 hours
    = 3hours, 25.7 minutes

    (notice the effective calculation was 1 รท (1/6 + 1/8)

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