a man swims downstream 72 km and upstream 45 km taking 10 hours each time ; what is the speed of the current ?
"72 - - - 10 ds = 7.2 ? - - - - 1 45 - - - - 10 us = 4.5 ? - - - - 1 s = ? s = ( 7.2 - 4.5 ) / 2 = 1.35 answer : d"
divide(add(divide(45, 10), divide(72, 10)), const_2)