a boat goes 100 km downstream in 10 hours , and 200 km upstream in 25 hours . the speed of the stream is ?
"100 - - - 10 ds = 10 ? - - - - 1 200 - - - - 30 us = 8 ? - - - - - 1 s = ( 10 - 8 ) / 2 = 1 kmph . answer : a"
divide(subtract(divide(100, 10), divide(200, 25)), const_2)