Question

A person covers 40% of his journey at 12 km/h and remaining at 8 km/h. what is his average speed for complete journey correct to one decimal place in km/h?
1. 9.2
2. 9.8
3. 9.4
4. 10

Answer 1

Correct Answer - Option 1 : 9.2

Given:

Speed of 40% = 12 km/h

Speed for remaining distance = 8 km/h

Formula used:

Speed = Distance/Time

Average speed = Total Distance/Total Time

Calculation:

Let the distance be x km

Speed at which 0.4xkm distance covered = 12km/h

Time = 0.4x/12 = x/30 hours

Speed at which 0.6xkm distance covered = 8 km/h

Time = 0.6x/8 = 3x/40 hours

Total time = x/30 + 3x/40 = (4x + 9x)/120 = 13x/120 hours

Average speed = \(\frac{x}{\frac{13x}{120}}\) = 120/13 = 9.2 km/h

∴ The average speed is 9.2 km/h