a man whose speed is 3.5 kmph in still water rows to a certain upstream point and back to the starting point in a river which flows at 1.5 kmph , find his average speed for the total journey ?
"m = 3.5 s = 1.5 ds = 5 us = 2 as = ( 2 * 5 * 2 ) / 5 = 4 answer : e"
divide(add(3.5, subtract(3.5, 1.5)), const_2)