an woman swims downstream 81 km and upstream 36 km taking 9 hours each time ; what is the speed of the current ?
81 - - - 9 ds = 9 ? - - - - 1 36 - - - - 9 us = 4 ? - - - - 1 s = ? s = ( 9 - 4 ) / 2 = 2.5 answer : c
divide(subtract(divide(81, 9), divide(36, 9)), const_2)