a man swims downstream 28 km and upstream 12 km taking 2 hours each time , what is the speed of the man in still water ?
"28 - - - 2 ds = 14 ? - - - - 1 12 - - - - 2 us = 6 ? - - - - 1 m = ? m = ( 14 + 6 ) / 2 = 10 answer : a"
divide(add(divide(12, 2), divide(28, 2)), const_2)