a man swims downstream 36 km and upstream 26 km taking 2 hours each time , what is the speed of the man in still water ?
"36 - - - 2 ds = 18 ? - - - - 1 26 - - - - 2 us = 13 ? - - - - 1 m = ? m = ( 18 + 13 ) / 2 = 15.5 answer : c"
divide(add(divide(26, 2), divide(36, 2)), const_2)