Aptitude Day 250

Answers of Day 249: 1. 12 minutes.

                                        2. 3 hours.

Problems on Pipes and cisterns:

1. Two pipes can fill a tank in 6 and 8 hours respectively and a waste pipe can empty 22 gallons per hour. All the 3 pipes working together can fill the tank in 5 hours. The capacity of the tank is:

Solution:

                  Part filled by (A+B+C) – Part filled by (A+B) in 1 hour = 1/5 – (1/6 + 1/8) = -11/120

                  Note: Negative sign indicates emptying.

                 Volume of 11/120 part = 22 gallons

                 Volume of the tank = 22*(120/11) = 240 gallons.

2. Two pipes A and B can fill the tank in 13(1/3) and 20 minutes respectively. Both pipes are opened. The tank will be filled in 10 minutes, if the pipe B is turned off after:

Solution:

                   Let B is turned off after x minutes.

                   x(3/40+ 1/20) +(10-x)3/40 = 1

                   x = 5 minutes.