* Can you solve the problem?

QUESTION:

A plane maintains an average speed of 285mph from London to New York. It then returns from New York to London at an average speed of 76mph. What is the average speed for the entire journey?

SOLUTION:

If the one-way distance was 1000 miles, the outward journey took 1000/285 hours and the return journey took 1000/76 hours. Therefore the total time taken was (1000/285 + 1000/76) hours for 2000 miles. So the average speed was 2000 / (1000/285 + 1000/76) which equals 120mph.
QED.