math

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it takes bill 4 hours to paint a house. it takes john 7 hours to paint the same house. how long does it take to paint the house if they painted it together.

  • math -

    7+4= 11/2 is equal to 9 and 1 half hours.

  • math -

    Oh heavens, it takes them longer working together Lu ????

    Bill paints 1/4 house per hour
    John paints 1/7 house per hour
    so together they paint
    1/4 + 1/ 7 = 7/28 + 4/28 = 11/28 houses per hour
    which is 28 /11 hours/house
    or around 2.55 hours
    or 2 hours and 33 minutes

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