a man swims downstream 72 km and upstream 45 km taking 12 hours each time ; what is the speed of the current ?
"72 - - - 12 ds = 6 ? - - - - 1 45 - - - - 12 us = 3.75 ? - - - - 1 s = ? s = ( 6 - 3.75 ) / 2 = 1.125 answer : a"
divide(add(divide(45, 12), divide(72, 12)), const_2)