A girl goes to school at a speed of 6 km/hr. She comes back with a speed of 18 km/hr. Find her average speed for the whole journey.

Correct option is B

Given:

Speed while going = 6 km/h

Speed while returning = 18 km/h

Formula Used:

When the distance is the same for both parts of the journey, the average speed is given by:

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

Solution:

Average speed = $$\frac{2 \times 6 \times 18}{6 + 18}$$​​

= $$\frac{216}{24}$$​​

= 9 km/h