Two pipes a and b separately fill in 15/2 min and 5 min respactively and third pipe c can empty of 14l/m if all the pipes are open when the cistern is full, it is emptied in 1 hr. how many litres does the cistern hold?  Choose the correct answer:
A) 40	B) 30	C) 50	D) 80	E) 54

Rationale: let total water in cistern = x liter speed of a = 2 x / 15 l / m ( speed = liter / time ) speed of b = x / 5 l / m speed of c = 14 l / m according to question x + ( x / 5 + 2 x / 15 ) * 60 = 60 * 14 x + = 60 * 14 x = 40 liter answer : a
Answer: A