3 Pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the same tank in 1 day ?

A 9

B 10

C 11

D 12

Correct Answer: Option D

3 pumps need 2 × 8 hours = 16 hours
1 pump needs 16 × 3 hours
4 pumps need (16 × 3)/4 hours
= 12 hours