find avrg speed if a man travels at speed of 24 km / hr up and 36 km / hr dawn at an altitude of 200 m .
avg speed = 2 * x * y / ( x + y ) = 2 * 24 * 36 / ( 24 + 36 ) = 28.8 answer : d
divide(multiply(multiply(const_2, 24), 36), add(24, 36))