A woman covers a certain distance by car at 75 km/h and immediately returns by the same car to the starting point at 100 km/h. What is the average speed of the car?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. km/h.
We know that,
Average speed = Total distance/Total Time
Let the distance of one way be D km
Now,
Time taken to cover D km at 75 km/hr = D/75 hours
Time taken to cover D km at 100 km/hr = D/100 hours
Total distance = 2D
Total time = D/75 + D/100 hrs
⇒ D(1/75 + 1/100)
⇒ D(4/300 + 3/300)
⇒ D × 7/300
Average speed = 2D/7D/300
⇒ (2D × 300)/7D
⇒ 600/7 km/hr = km/hr
So, the average speed of the car for the entire trip is approximately km/hr