talaangoshtari wrote:A,B, and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?
A.13
B.14
C.15
D.16
E.17
Let the job = 60 widgets.
Since A takes 20 days, A's rate = w/t = 60/20 = 3 widgets per day.
Since B takes 30 days, B's rate = w/t = 60/30 = 2 widgets per day.
Since C takes 60 days, B's rate = w/t = 60/60 = 1 widget per day.
Combined rate for A+B+C working together = 3+2+1 = 6 widgets per day.
Over the course of 3 days:
Work done by A in the first 2 days = r*t = 3*2 = 6 widgets.
Work done by A, B and C on the 3rd day = 6 widgets.
Total widgets produced in 3 days = 6+6 = 12 widgets.
Since 12 widgets are produced in 3 days, 60 widgets -- 5 times the amount of work -- will take 5 times as long:
5*3 = 15 days.
The correct answer is
C.
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