Question

A car drove from Mumbai to Pune without stopping. It covered the first 72 km of its journey at an average speed of 48 km/h. What was the car’s average speed (in km/h), for the remaining 63 km if its overall average speed was 27 km/h?

1. 21 km/h
2. 18 km/h
3. 16 km/h
4. 14 km/h

Answer 1

Correct Answer - Option 2 : 18 km/h

Given:

First distance covered = 72 km

1st average speed = 48 km/h

Second distance covered = 48 km

Overall average speed = 27 km/h

Formula used:

Average speed = (Total distance traveled)/(Total time is taken)

Calculation:

Let V be the average speed of the car in the second half of travel.

As we know, overall average speed of the car = (Total distance covered)/(Total time taken)

⇒ 27 = (72 + 63)/(72/48 + 63/V)

⇒27 = 135/(1.5 + 63/V)

⇒ 1.5 + 63/V = 135/27 = 5

⇒ 63/V = 5 – 1.5 = 7/2

⇒ V = 9 × 2 = 18 km/h

∴ The average speed of second distance covered is 18 km/h.