1. Two pipes A & B can fill a tank in 20 and 30 minutes respectively.If the both pipes are used together,then how long will it take to fill the tank?

A. 12 mins B. 15 mins C. 25 mins D. 50 mins

Answer Answer: Option A Explanation: Part filled by A in 1 minute = 1/20; Part filled by B in 1 minute = 1/30.
Part filled by (A+B) in 1 minute.
(A+B) = (1/20+1/30) = 1/12.
Hence both the pipes can fill the tank in 12 minutes

2. A cistern can be filled by a tape in 4 hrs while it can be emptied by another tape in 9 hrs. If both the tapes are opened simultaneously then after how much time will the cistern get filled?

A. 4.5 hrs B. 5 hrs C. 6.5 hrs D. 7.2 hrs

Answer Answer: Option D Explanation: Net part filled in 1 hr = (1/4 - 1/9) = 5/36.
The cistern will be filled in 36/5 hrs i.e. 7.2 hrs

3. A tape can fill a tank in 6hrs.After half the is filled 3 more similar tapes are opened.What is total time taken to fill the tank completely?

A. 3hrs 15 minutes B. 3hrs 45 mins C. 4 hrs 15 mins D. 4 hrs

Answer Answer: Option B Explanation: Time taken by 1 tape to fill half the tank = 3hrs.
Part filled by the 4 tapes in 1 hr = (4*1/6) = 2/3.
Remaining part = (1-1/2) = 1/2
2/3: 1/2: 1: x or x =(1/2*1*3/2) = 3/4 hrs i.e.45 minutes
so total time taken 3 hrs 45 mins.

4. A water tank is 2/5th full.Pipe A can fill a tank in 10 mins and pipe B can empty it in 6 mins. If both the pipes are open,how long will it take to empty or fill the tank completely?

A. 6 mins to empty B. 6 mins to fill C. 9 mins to empty D. None of these

Answer Answer: Option A Explanation: clearly pipe B is faster than Pipe A and so the tank will be emptied.
Part to be emptied = 2/5
Part emptied by (A+B) in 1 minute = (1/6 - 1/10) = 1/15
hence 1/15 : 2/5 : :1:x or x=(2/5*1*15) = 6 mins
so the tank will be emptied in 6 mins

5. Pipe A can fill a tank in 5 hrs, Pipe B in 10 hrs and Pipe C in 30 hrs.If all the pipes are open in how many hours will the tank be filled?

A. 2 hrs B. 2.5 hrs C. 3 hrs D. 3.5 hrs

Answer Answer: Option C Explanation: Part filled by ( A+B+C) in 1 hr = (1/5+1/10+1/30) = 1/3
therefore all the 3 pipes together will fill the tank in 3 hrs