Let D be the distance between point A and point B. Time taken to travel from A to B (T1) = Distance / Speed = D / 20 hours. Time taken to travel from B to A (T2) = Distance / Speed = D / 30 hours. The total travel time for the round trip is 5 hours, so T1 + T2 = 5. Substitute the expressions for T1 and T2: D/20 + D/30 = 5. To add the fractions, find a common denominator for 20 and 30, which is 60. (3D/60) + (2D/60) = 5. Combine the terms: (3D + 2D) / 60 = 5. 5D / 60 = 5. Simplify the fraction: D / 12 = 5. Multiply both sides by 12 to solve for D: D = 5 * 12. Therefore, D = 60 km. Why others are wrong: A — Correct. B — This could result from a calculation error, such as using an incorrect common denominator or a miscalculation in simplifying the equation. C — This would be the result if one incorrectly assumed that the cyclist spent an equal amount of time (2.5 hours) on each leg of the journey and then calculated the distance using only the higher speed (30 km/h * 2.5 h = 75 km). D — This represents the total distance for the entire round trip (2 * 60 km = 120 km), not the one-way distance between A and B.