1.) Two pipes can fill a tank in 10 hours and 12 hours respectively while a third, pipe empties the full tank in 20 hours. If all the three pipes operate simultaneously, in how much time will the tank be filled?

**A.** 4 hrs 30 min **B.** 7 hrs 30 min

**C.** 8 hrs 10 min **D.** None of these

**View Answer**

**Answer:** Option **B**

**Explanation:**

Net part filled in 1 hour = (1/10) + (1/12)-(1/20) = (8/60) = (2/15).

The tank will be full in 15/2 hrs = **7 hrs 30 min.**

2.)** **An electric pump can fill a tank in 3 hours. Because of a leak in, the tank it took 3(1/2) hours to fill the tank. If the tank is full, how much time will the leak take to empty it?

**A.** 14 hours **B.** 16 hours

**C.** 18 hours **D.** 21 hours

**View Answer**

**Answer:** Option **D**

**Explanation:**

Work done by the leak in 1 hour= (1/3)-(1/ (7/2))

= (1/3)-(2/7) = (1/21).

The leak will empty .the tank in **21 hours.**

** **

3.) Two pipes A and B can fill a tank in 36 min. and 45 min. respectively. A water pipe C can empty the tank in 30 min. First A and B are opened. After 7 min, C is also opened. In how much time, the tank is full?

**A.** 17 min **B.** 24 min

**C.** 28 min **D.** 39 min

**View Answer**

**Answer:** Option **D**

**Explanation:**

Part filled in 7 min. = 7*((1/36) + (1/45)) = (7/20).

Remaining part= (1-(7/20)) = (13/20).

Net part filled in 1 min. when A, B and C are

opened= (1/36) + (1/45)-(1/30) = (1/60).

Now, (1/60) part is filled in one minute.

(13/20) part is filled in (60*(13/20)) =**39 minutes.**

4.) Two pipes A, B can fill a tank in 24 min. and 32 min. respectively. If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 min.?

**A.** 5 min **B.** 14 min

**C.** 8 min **D.** 19 min

**View Answer**

**Answer:** Option **C**

**Explanation:**

Let B be closed after x min. then,

Part filled by (A+B) in x min. +part filled by A in (18-x) min = 1

Therefore x*((1/24) + (1/32)) + (18-x)*(1/24) =1

==> (7x/96) + ((18-x)/24) =1.

==> 7x +4*(18-x) =96.

Hence, be must be closed after **8 min.**

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

**A.** 12 min **B.** 15 min

**C.** 25 min **D.** 50 min

**View Answer**

**Answer:** Option **A**

**Explanation:**

Part filled by A in 1 min = 1/20

Part filled by B in 1 min = 1/30

Part filled by (A + B) in 1 min = (1/20 **+** 1/30) = 1/12

Both pipes can fill the tank in **12 minutes.**