From the top of a vertical cliff 40 m high, two buoys floating in line with the foot of the cliff are seen at angles of depression of 60° and 30°. The distance between the two buoys is:

The buoys lie 40·cot60° = 40/√3 ≈ 23.1 m and 40·cot30° = 40√3 ≈ 69.3 m from the foot of the cliff, so the gap between them is 40√3 − 40/√3 = 80/√3 = 80√3/3 ≈ 46.2 m. The choice 40√3 is the far buoy's own distance and 40√3/3 = 40/√3 the near buoy's; adding the two distances (which would be right only if they lay on opposite sides of the cliff) gives about 92.4 m.