A train travels from A to B at speed of x km/hour and from B to A at speed of y km/hour. The average speed of the train from A to B and back to A, would be calculated by the

Question

$(a)\;Arithmetic\;mean\qquad(b)\;Geometric\;mean\qquad(c)\;Harmonic\;mean\qquad(d)\;None\;of\;the\;above$