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?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 78.75 km/h.
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
The average speed = Total distance/total time covered = 2xy/(x + y)
where, x = the speed of the bus from P to Q
y = the speed of the bus from Q to P
The average speed = 2 × 70 × 90/(70 + 90) = 140× 90/160 = 1260/16 = 78.75 km/h