a man swims downstream 40 km and upstream 16 km taking 4 hours each time , what is the speed of the man in still water ?
"40 - - - 4 ds = 10 ? - - - - 1 20 - - - - 4 us = 5 ? - - - - 1 m = ? m = ( 10 + 5 ) / 2 = 7.5 answer : b"
divide(add(divide(16, 4), divide(40, 4)), const_2)