a boy swims downstream 91 km and upstream 21 km taking 7 hours each time , what is the speed of the boy in still water ?
91 - - - 7 ds = 13 ? - - - - 1 21 - - - - 7 us = 3 ? - - - - 1 m = ? m = ( 13 + 3 ) / 2 = 8 answer : c
multiply(divide(const_1, const_2), add(divide(91, 7), divide(21, 7)))