Question

A person in a car drives along a straight road from point A to point B at a speed of 60 km/hour for 15 minutes and then from point B to point C at a speed of 90 km/hour for 10 minutes. The average speed of his travel from point A to C is

1. 75 km/hr
2. 72 km/hr
3. 68 km/hr
4. 78 km/hr

Answer 1

Correct Answer - Option 2 : 72 km/hr

Formula used:

Average speed = Total distance/Total time

Distance = Speed × Time

Calculation:

Distance from A to B = 60 × (15/60) = 15 km 

Distance from B to C = 90 × (10/60) = 15 km

Average speed = (15 + 15)/(15/60 + 10/60) = 72 km/hr

∴ The average speed of his travel from point A to C is 72 km/hr