Question

Mark averaged 60 miles per hour during the 30-mile trip to college. Because of heavy traffic he was able to average only 20 miles per hour during the return trip. What was Mark's average speed for the round trip?

Answer 1

Mark averaged 60 miles per hour during the 30 mile trip to college.

Now, if he goes 60 miles in 1 hour, then the 30 mile trip to college will take Mark 30/60=0.5 hours.

During the return trip, he could only average 20 miles per hour.

Now, if he goes 20 miles in 1 hour, then the 30 mile return trip from college will take 30/20=1.5 hours.

So, the total distance Mark travels back and forth is 30+30, ie. 60 miles.

The total time Mark takes for this round trip, is 0.5+1.5, ie. 2 hours.

So, Mark's average speed in the round trip is

=60/2

=30 miles per hour.

The answer is

Mark's average speed during the round trip is 30 miles per hour.