2018 · Q48
A car has an average speed of 60 km per hour while going from Delhi to Agra and has an average speed of y km per hour while returning to Delhi from Agra (by travelling the same distance). If the average speed of the car for the whole journey is 48 km per hour, then what is the value of y?
Elementary MathematicsTime, Speed and Distance
- A30 km per hour
- B35 km per hour
- C40 km per hour
- D45 km per hour
Explanation
For equal distances, average speed is the harmonic mean: 2 × 60y/(60 + y) = 48. Then 120y = 2880 + 48y gives 72y = 2880, so y = 40 km/h, option (C).