SOLUTION: jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 7 hours. How much time would it take for them to mow the lawn together?

Question 315624: jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 7 hours. How much time would it take for them to mow the lawn together?
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
in some time (t), Jack will mow t/3 of the lawn
___ during the same time, Marilyn will mow t/7 of the lawn
___ these two fractions add up to the whole lawn

(t/3) + (t/7) = 1

multiplying by 21 (LCD) ___ 7t + 3t = 21

10t = 21 ___ t = 2.1
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