1. ** **Pipe A can fill a tank in 2hr, pipe B in 4 hrs and pipe C in 6 hrs**. **If all the pipes are open, in how many hours the tank will fill?

**(a) **

**(b) **

**(c) **

**(d)**

**Answer: (a)**

**Explanation:**

Part filled by A in 1 hr

Part filled by B in 1 hr

Part filled by C in 1 hr

Part filled by A+B+C in 1 hr

All the pipes together will fill the tank in hours.

2. ** **Tap A can fill a water tank in 25 min, tap B can fill the same tank in 40 min and tap C can empty that tank in 30 min**. **If all the three taps are opened together, in how many min will the tank be completely filled up or emptied? (Bank PO 2001)

**(a) **

**(b) **

**(c) **

**(d)**

**Answer: (d)**

**Explanation:**

Part filled by A+B+C in 1 hr

The tank will be full in

3. Two pipes A and B can fill a tank in 16 hours and 24 hours respectively**. **If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 hours?

**(a) **2 hrs

**(b) **4 hrs

**(c) **8 hrs

**(d) **16 hrs

**Answer: (c)**

**Explanation:**

Let B closed after x hours**. **Then,

Part filled by (A+B) in x hours

Part filled by A in (18-x) hours

Part filled by (A+B) in x hours + Part filled by A in (18-x) hours = 1

5x+54-3x-48 = 0

2x-16 = 0

x = 8 hours**.**

Hence, B must be closed after 8 hours**.**

4. Two pipes A and B can fill a cistern in 12 mins and 15 mins respectively, but a third pipe C can empty the full tank in 6 mins**. **A and B are kept open for 5 min in the beginning and then C is also opened**. **In what time is the cistern emptied? (Bank PO 2000)

**(a) **30 mins

**(b) **33 mins

**(c) **37**. **5 mins

**(d) **45 mins

**Answer: (d)**

**Explanation:**

Work done by A in 1 min

Work done by B in 1 min and

Work done by C in 1 min

Therefore, work done in first 5 min

Now, C is also opened**.**

Then, A, B and C together will empty this tank**.**

Now, work done by A, B and C together

5**. **A tank is filled in 10 hrs by three pipes A, B and**(c) **The pipe C is twice as fast as B and B is twice as fast as**(a) **How much time will pipe A alone take to fill the tank? (SSC Grad 2000)

**(a) **10 hrs

**(b) **40 hrs

**(c) **70 hrs

**(d) **80 hrs

**Answer: (c)**

**Explanation:**

Let pipe A alone fill the tank in x hrs**.**

Then, pipe B will fill it in

Pipe C will fill it in

x=70hrs

6**. **Pipe A can fill a tank in 2hrs, pipe B in 4 hrs and pipe C in 6 hrs**. **If all the pipes are open, in how many hours the tank will fill?

**(a) **

**(b) **

**(c) **20 hrs

**(d) **3 hrs

**Answer: (a)**

**Explanation:**

Part filled by A in 1 hr

Part filled by B in 1 hr

Part filled by C in 1 hr

Part filled by A+B+C in 1 hr

All the pipes together will fill the tank in hours .

7**. **A cistern has 3 pipes A, B and C** **The pipes A and B can fill it in 5 hr and 6 hr respectively and C can empty it in 3 hr**. **If the pipes are opened in order at 3 pm, 4 pm and 5 pm respectively at what time the tank be filled?

**(a) **6 am

**(b) **5 am

**(c) **4 am

**(d) **7 am

**Answer: (a)**

**Explanation:**

By 5 pm, the water filled by 2 pipes = 2 hr work done by pipe + 1 hr work done by pipe B

After 5 pm all the three pipes are working and the work done by all the 3 pipes 1 hr

After 5pm only of the tank is to be filled time taken in filling

13 hr after 5 pm = 6 am

8**. **Three pipes A, B and C can fill a tank in 12 hrs**. **After working at it together for 4 hrs, C is closed and A and B can fill the remaining part in 14 hrs**. **The number of hours taken by C alone to fill the tank is:

**(a) **10 hrs

**(b) **12 hrs

**(c) **14 hrs

**(d) **28 hrs

**Answer: (d)**

**Explanation:**

Part filled in 4 hrs

Remaining part

(A+B)’s 14 hrs work

(A+B)’s 1 hrs work

C’s 1hrs work= (A+B+C)’s 1 hrs work-(A+B)’s 1 hrs work

C alone can fill the tank in 28 hrs**.**

9**. **A tank is filled in 2hrs by three pipes A, B and**(c) **The pipe C is three times as fast as B and B is twice as fast as**(a) **How much time will pipe A alone take to fill the tank?

**(a) **10 hrs

**(b) **12 hrs

**(c) **18 hrs

**(d) **80 hrs

**Answer: (c)**

**Explanation:**

Let pipe A alone fill the tank in x hrs**.**

Then, pipe B will fill it in

Pipe C will fill it in

x=18hrs.

10**. **Two pipes A and B can fill a cistern in 24min and 30min respectively, but a third pipe C can empty the full tank in 12 min**. **A and B are kept open for 10 min in the beginning and then C is also opened**. **In what time is the cistern emptied?

**(a) **2 hrs

**(b) **

**(c) **

**(d) **20 hrs

**Answer: (b)**

**Explanation:**