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If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

  • math -

    Sally can paint 1/4 of a house per hour.
    John can paint 1/6 of a house per hour.
    Let's say the answer is t hours for the total job.
    Then (1/4)t + (1/6)t = 1
    (1/4 + 1/6)t = 1
    (6/24 + 4/24)t = 1
    (10/24)t = 1
    t = 24/10 hours = 2.4 hours

  • math -

    If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

    This is the ans. 2 hours and 24 minutes
    But how they work it out?

  • math -

    What don't you understand about Diana's solution?

    Here is another way to look at it:

    Consider the equation: job = rate x time , or rate = job/time or time = job/rate

    sally" rate = job/4
    john's rare = job/6
    combined rate = job/4 + job/6
    = 5job/12

    time at that rate = job/(5job/12) = 12/5 - 2.4

  • math -

    From Diana's solution,

    2.4 hrs = 2 hrs 24 min

    To convert .4 hrs to minutes, multiply by 60.
    .4 hrs * 60 min = 24 min

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