a man swims downstream 18 km and upstream 12 km taking 3 hours each time , what is the speed of the man in still water ?
"18 - - - 3 ds = 6 ? - - - - 1 12 - - - - 3 us = 4 ? - - - - 1 m = ? m = ( 6 + 4 ) / 2 = 5 answer : b"
divide(add(divide(12, 3), divide(18, 3)), const_2)