SSC CGL 2024 PYQ — Question 63

The correct answer is option 3 i.e. 10:48 a.m.

Pipe A fills the tank in 4 hours  → Rate of A =  1/4  tank per hour  

Pipe B fills the tank in 6 hours → Rate of B = 1/6 tank per hour  

Work Done by Pipe A Alone from 8:00 a.m. to 9:00 a.m.  

⇒ 1/4

Thus, by 9:00 a.m., 1/4  of the tank is filled.

Work Done by Both Pipes A and B Together  

⇒ 1/ 4 + 1/ 6

⇒ $\frac{1}{4} = \frac{3}{12}, \quad \frac{1}{6} = \frac{2}{12}$

⇒ $\frac{3}{12} + \frac{2}{12} = \frac{5}{12}$

 Time Required to Fill the Remaining Tank  

⇒ $1 - \frac{1}{4} = \frac{3}{4}$

Time  = $\frac{\frac{3}{4}}{\frac{5}{12}} = \frac{3}{4} \times \frac{12}{5} = \frac{36}{20} = 1.8$ hours

1.8 hours = 1 hour 48 minutes  

 Pipe B was opened at 9:00 a.m.  

 After 1 hour 48 minutes, the tank will be full.  

Thus, the tank will be completely filled at 10:48 a.m..