a man rows his boat 90 km downstream and 45 km upstream , taking 2 1 / 2 hours each time . find the speed of the stream ?
"speed downstream = d / t = 90 / ( 2 1 / 2 ) = 36 kmph speed upstream = d / t = 45 / ( 2 1 / 2 ) = 18 kmph the speed of the stream = ( 36 - 18 ) / 2 = 9 kmph answer : a"
divide(subtract(divide(90, 2), divide(45, 2)), const_2)