a man swims downstream 72 km and upstream 45 km taking 5 hours each time ; what is the speed of the current ?
"72 - - - 5 ds = 14.4 ? - - - - 1 45 - - - - 5 us = 9 ? - - - - 1 s = ? s = ( 14.4 - 9 ) / 2 = 2.7 answer : d"
divide(add(divide(45, 5), divide(72, 5)), const_2)