Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in: Choose the correct choice
A) 6 hours  B) 20/3hours  C) 7 hours  D) 15/2hours  E) 17/2hours
Taking the lcm(12,15,20) = 60 liters (capacity of the tank)   In 1 hr : A can fill 5 liters(60/12), B = 4 liters C = 3 liters   Its given that A is open all time and B &amp; C alternately.   So in 1st hr : A+B = 9 liters   2nd hr : A+7 hours = 8 liters   3rd hr : A+B = 9 liters   4th hr : A+7 hours = 8 liters   5th hr : A+B = 9 liters   6th hr : A+7 hours = 8 liters   7th hr : A+B = 9 liters   Total = 60 liters   ANSWER:7 hours
<result>C</result>
Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in: