3 grade math

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if a man cut grass in 6 hour , another man cut in 12 hour , how many hour ther were both spend if they cut grass toghter.
answer 9 hour or 4 hour

  • plz answer ....plz -

    plz answer ....plz

  • 3 grade math -

    rate of first man = 1/6 lawn/hr
    rate of 2nd man = 1/12 lawn/hr
    combined rate = 1/6 + 1/12 = 3/12 or 1/4 lawn/h

    time takes when both cutting = 1/(1/4)
    = 1 (4/1) = 4 hrs

    (how can the combined work take 9 hours, if one guy alone can do it in 6 hrs??)

  • 3 grade math -

    thank you so much .........

  • 3 grade math -

    12+6=18

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