A boy traveled from Dhaka to Comilla at 20kmph and from Comilla to Dhaka at 30kmph. What is his average speed?

Question: A boy traveled from Dhaka to Comilla at 20kmph and from Comilla to Dhaka at 30kmph. What is his average speed?

Solution:
Let,
Distance from Dhaka to Comilla = P
From Dhaka to Comilla,
speed = 20kmph
∴ time = P/20 hour

From Comilla to Dhaka,
speed = 30kmph
∴ time = P/30 hour

Average speed = total distance/total time
= 2P/(P/20 + P/30)
= 24 kmph