A girl goes to school at a speed of 28 km/hr. She comes back with a speed of 21 km/hr. Find her average speed for the whole journey.

Correct option is C

Given:

Speed while going = 28 km/hr

Speed while coming back = 21 km/hr

Find: Average speed for the whole journey (equal distance)

Formula Used:

Average Speed = $$\frac{2ab}{a + b}$$​​

Average Speed = $$\frac{2 \times 28 \times 21}{28 + 21}$$​​

Solution:

Average Speed = $$\frac{2 \times 28 \times 21}{49}$$​​

= $$\frac{1176}{49}$$ = 24 km/hr