a boy walks to his school at a distance of 6km with constant speed of 2.5 k mph and walks back with a constant sped of 4 k mph. His average speed of round trip expressed in k mph is?

Answer 1

Time out = 6/2.5 = 2.4 hours
Time back = 6/4 = 1.5 hours
Average speed for the round trip =
(6 + 6/(2.4 + 1.5) = 3.077 kmph

Answer 2

Av speed = Total Distance/Total Time
= 6+6/(6/2.5 + 6/4)
On solving the equation we get Average Speed = 3.07kmph or 40/13 kmph