a man swims downstream 51 km and upstream 18 km taking 3 hours each time , what is the speed of the man in still water ?
"51 - - - 3 ds = 17 ? - - - - 1 18 - - - - 3 us = 6 ? - - - - 1 m = ? m = ( 17 + 6 ) / 2 = 11.5 answer : e"
divide(add(divide(18, 3), divide(51, 3)), const_2)