Correct Answer - Option 1 : 12 min

**Given:**

Tank filled by A = 36 min

Tank filled by B = 45 min

Total time taken to fill the tank = 30 min

**Formula used:**

Efficiency × Time taken = Total capacity of tank

**Calculation:**

LCM OF 36 and 45 = 180 unit = Total capacity of tank

Time taken by A to fill the tank = 180/36 = 5 unit

Time taken by B to fill the tank = 180/45 = 4 unit

Pipe A is closed after x times but Pipe B is opened for 30 mins

Tank filled by Pipe B = 30 × 4 = 120

Remaining units to be filled = 180 – 120 = 60 units

Remaining 60 units was filled by pipe A

Time taken by Pipe A = 60/5

⇒ 12 min

**∴ The value of x is 12 min**