a man swims downstream 60 km and upstream 40 km taking 4 hours each time ; what is the speed of the current ?
"explanation : 60 - - - 4 ds = 15 ? - - - - 1 40 - - - - 4 us = 10 ? - - - - 1 s = ? s = ( 15 - 10 ) / 2 = 2.5 answer : option b"
divide(add(divide(40, 4), divide(60, 4)), const_2)