A, B two inlet pipes takes 15,18 minutes to fill the tank and C an oulet pipe takes 45 minutes to empty the tank respectively. In what time the tank be filled if all of them are operated together? Choose the correct choice from the following answers:
A) 11 minutes B) 10 minutes C) 12 minutes D) 13 minutes E) 14 minutes

Rationale: lcm = 90 no of days = [ 90 / ( 90 / 15 + 90 / 18 - 90 / 45 ) = [ 90 / ( 6 + 5 - 2 ) ] = [ 90 / 9 ] = 10 minutes answer : b
Answer: B