A train goes from A to B at a speed of 12 km/h and returns from B to A by the same route at 24 km/h. The average speed (in km/h) of the train during the two-way journey is:

Correct option is C

Explanation of options: (a) ✘ 13 is an incorrect approximation and doesn’t follow the formula. (b) ✘ 18 is closer to the higher speed but incorrect as average. (c) ✔ Correctly computed using harmonic mean formula for equal distances. (d) ✘ 14 is a miscalculated average not based on the correct method.