a man swims downstream 30 km and upstream 18 km taking 6 hours each time , what is the speed of the man in still water ?
"30 - - - 6 ds = 5 ? - - - - 1 18 - - - - 6 us = 3 ? - - - - 1 m = ? m = ( 5 + 3 ) / 2 = 4 answer : e"
divide(add(divide(18, 6), divide(30, 6)), const_2)