3 identical taps can fill a tank at the speed of 10 litre/per minute each. They are opened simultaneously when the tank is empty at 10:00 am and stopped at 11:40 am. An pipe with a emptying speed of 30 litre per minute is started at 12:00 pm. At what time will it empty the tank completely?

1:40 pm

The correct answer is Option (4) → 1:40 pm

$\text{Filling rate} = 3 \times 10 = 30 \text{ L/min}$

$\text{Time of filling} = 10:00 \text{ to } 11:40 = 100 \text{ minutes}$

$\text{Total water filled} = 30 \times 100 = 3000 \text{ litres}$

$\text{Emptying rate} = 30 \text{ L/min}$

$\text{Time to empty} = \frac{3000}{30} = 100 \text{ minutes}$

$\text{Starting at } 12:00 \text{ pm}$

$\text{Ending time} = 12:00 + 100 \text{ min} = 1:40 \text{ pm}$

The tank will be empty at 1:40 pm.