2026 · Q16
A train P starts from station X for station Y and another train Q starts from station Y for station X at the same time. After passing each other, P takes 4 hours to reach Y and Q takes 1 hour to reach X. If the average speed of P is 60 km/h, then what is the average speed of Q?
Elementary MathematicsTime, Speed and Distance
- A72 km/h
- B80 km/h
- C96 km/h
- D120 km/h
Explanation
For two bodies starting simultaneously toward each other, the ratio of speeds equals the square root of the inverse ratio of their post-meeting travel times: vP/vQ=√(tQ/tP)=√(1/4)=1/2. With vP=60 km/h, vQ=120 km/h, option D. Inverting the square root gives the distractor 30 km/h.