Two-thirds of a certain distance was covered at the speed of 45 km/h, one-fourth at the speed of 60 km/h and the rest at the speed of 75 km/h. Find the average speed per hour for the whole journey. (correct to 2 decimal places)
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 49.77 km/h
Formula used:
Average speed = total distance/total time
Calculations:
⇒ Let the whole distance be 12x
Time taken to complete two third of the distance = 8x/45
Time taken to complete one fourth of the distance = 3x/60
Time taken to complete rest distance = x/75
Using the given formula;
⇒ Required speed = 12x/(8x/45 + x/20 + x/75)
⇒ (12 × 900)/(160 + 45 + 12)
⇒ 10800/217
⇒ 49.77 km/h