A bus travels from station P to station Q at a speed of 70 km/h, and from station Q to station P at a speed of 90 km/h. What is the average speed of the bus during the entire journey?

Correct option is B

Given:
Speed from station P to station Q: 70 km/h
Speed from station Q to station P: 90 km/h
Formula Used:
Average speed = $$\frac{2xy}{x + y}$$​​
Solution:
Average speed = $$\frac{2 \times 70 \times 90}{70 + 90} = 78.75\, \text{km/hr}$$​ = 78.75 km/h