Question

Pipe A can fill a cistern in 36 minutes and B in 48 minutes. If both the pipes are opened together, when should pipe B be closed so that the cistern may be just full in 24 minutes?
1. 8 mins
2. 9 mins
3. 12 mins
4. 16 mins

Answer 1

Correct Answer - Option 4 : 16 mins

Given:

A fill a cistern in 36 minutes

B fill a cistern in 48 minutes

Cistern is filled in 24 minutes

Formula Used:

Efficiency ×  Time taken = Total capacity of tank

Total capacity of cistern = LCM of time taken

Calculation:

Total capacity of cistern = LCM of 36 and 48

⇒ Total capacity of cistern = 144 units

Time taken by A to fill cistern = 144/36 = 4

Time taken by B to fill cistern = 144/48 = 3

Pipe B is closed after some time, but pipe A worked for 24 minutes,

In 24 minutes,

Cistern filled by pipe A = 24 × 4 = 96

Remaining units to be filled,

⇒ 144 – 96 = 48

Remaining 48 units was filled by pipe B,

Time taken by pipe B,

⇒ 48/3 = 16 minutes.

∴ Pipe B closed after 16 minutes.