Taps three times A, B, and C can each fill a tank in 12, 15, and 20 hours. The tank will be full in: if A is open all the time and B and C are open for one hour each alternately.
A. 6 hours
B. 6 2/3 hours
C. 7 hours
D. 7 1/2 hours
Answer:C
Taps three times A, B, and C can each fill a tank in 12, 15, and 20 hours. The tank will be full in: if A is open all the time and B and C are open for one hour each alternately.
A. 6 hours B. 6 2/3 hours C. 7 hours D. 7 1/2 hours
Explanation: 1 hour of labour (A + B) =1/12+1/15=9/60 3/20.Hours worked by (A + C) = 1/12+1/20= 8/60=2/15..Part completed in 2 hours = 3/20 + 2/15 = 17/60..Part completed in 6 hours = 3 x 17/60 = 17/20.The remaining portion is 1 - 17/20 = 3/20.Now it's A and B's turn, and they fill 3/20 of the portion in 1 hour.The total time it took to fill the tank was (6 + 1) hours, which equaled 7 hours.