find avrg speed if a man travels at speed of 16 km / hr up and 30 km / hr dawn at an altitude of 200 m .
"avg speed = 2 * x * y / ( x + y ) = 2 * 16 * 30 / ( 16 + 30 ) = 20.8 answer : c"
divide(multiply(multiply(const_2, 16), 30), add(16, 30))