Question

A car travels from Kanpur to Delhi at an average speed of 60 km/h and returns at an average speed of 90km/h. Find the average speed of the car in the whole journey.

• A. 65 km/h
• B. 78 km/h
• C. 60 km/h
• D. 72 km/h

Answer 1

Answer:

D. 72 km/h

When distances are the same, average speed is not the simple average. Instead, we use the formula:

$\text{Average speed} = \frac{2xy}{x + y}$

Here:

• (x = 60) km/h (Kanpur → Delhi)

• (y = 90) km/h (Delhi → Kanpur)

  $\text{Average speed} = \frac{2 \times 60 \times 90}{60 + 90}$
  $= \frac{10800}{150}$
  $= 72 \text{ km/h}$