a rower whose speed is 9 km / hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 3 km / hr . what is the rower ' s average speed ( in km / hr ) for the total journey ?
"time upstream = d / 6 time downstream = d / 12 total time = d / 6 + d / 12 = d / 4 average speed = 2 d / ( d / 4 ) = 8 km / hr the answer is b ."
divide(add(subtract(9, const_0.5), add(9, 3)), const_2)