Problem - 4692
$\textbf{Average Speed}$
Joe travels at an average of $30$ miles per hour from home to visit a friend who lives $60$ miles away. How fast should he drive on his way straight back to home so that his average speed is $60$ miles per hour for this entire trip?
$\textbf{Answer}$
It is impossible.
$\textbf{Analysis}$
The entire trip is $120$ miles in total. At an average speed of $60$ miles per hour, it will take $2$ hours to complete the entire trip. However, Joe has already spent $2$ hours driving to his friend's home. Therefore, this goal is unachievable.
$\textbf{Note}$
It is not a math problem, but a brain teaser. Therefore, watch out the traps.