A can fill tank in 9 minutes, B can empty the tank in 18 minutes.. In what time the tank be filled, if both pipes work simultaneously? Choose the correct choice:
A) 14 minutes B) 15 minutes C) 16 minutes D) 17 minutes E) 18 minutes

Rationale: bigger no = 18 , ratio = 9 : 18 = 1 : 2 time taken to fill the tank = 18 / ( 2 - 1 ) = 18 minutes answer : e
Answer: E