Question

14. Pipes A, B and C can fill a tank in 12, 15 and 20 hours
respectively. IfA is open all the time and B and C are open for
one hour each alternately, the tank will be full in
(a) 5 hrs
(b) 6 yrs
(c) 8 hrs
(d) 7 hrs​

Answer 1

Answer:

7 Hrs

Step-by-step explanation:

A can fill Tank in 1hr = 1/12

A can fill tank in 2 hr = 2/12 = 1/6

B & C alternate

B & C in 2 hr can fill = 1/15 + 1/20  =  (4 + 3)/60 = 7/60

A , B & C work in 2 hrs = 1/6 + 7/60  = 17/60

Work done in 2 * 3 = 6 hrs = 3 * 17/60 = 17/20

Work left = 1 - 17/20 = 3/20

Work done by A & B in 1 hr = 1/12 + 1/15  = (5 + 4)/60 = 9/60 = 3/20

so total time = 6 + 1 = 7 Hrs