Richa travels from A to B at the speed of 15 km/h, from B to C at 20 km/h, and from C to D at 30 km/h If (AB = BC = CD), then find the Richa's average speed.

When distances are equal, average speed is the harmonic mean: Average speed = Total distance ÷ Total time. Let distance = d. Time for each segment = d/15, d/20, d/30. Total time = d(1/15 + 1/20 + 1/30) = d(9/60) = 3d/20. Average speed = 3d ÷ (3d/20) = 20 km/h. Options A (17), B (19), and D (18) are incorrect because they use arithmetic mean or other wrong methods.