a man swims downstream 42 km and upstream 18 km taking 3 hours each time , what is the speed of the man in still water ?
"42 - - - 3 ds = 14 ? - - - - 1 18 - - - - 3 us = 6 ? - - - - 1 m = ? m = ( 14 + 6 ) / 2 = 10 answer : e"
divide(add(divide(18, 3), divide(42, 3)), const_2)