If a boat is rowed downstream for 500 km in 5 hours and upstream for 240 km in 6 hours, what is the speed of the boat and the river?
Pick: A) 70 , 30 B) 30 , 70 C) 70 , 70 D) 30 , 30 E) 80 , 50

Rationale: "explanation : if x : speed of boats man in still water y : speed of the river downstream speed ( ds ) = x + y upstream speed ( us ) = x â € “ y x = ( ds + us ) / 2 y = ( ds â € “ us ) / 2 in the above problem ds = 100 ; us = 40 x = ( 100 + 40 ) / 2 = 140 / 2 = 70 km / hr y = ( 100 - 40 ) / 2 = 60 / 2 = 30 km / hr answer : a"
Answer: A