Question 611030
    A can mow a lawn in 130 minutes, B takes 100 minutes and C takes 150 minutes. How long will it take all three, if they work together mowing the same lawn?
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Let x = time (minutes) for all three
then
x(1/130 + 1/100 + 1/150) = 1
multiplying both sides by 10:
x(1/13 + 1/10 + 1/15) = 10
multiplying both sides by 390:
x(30 + 39 + 26) = 3900
x(95) = 3900
x = 41.1 minutes