Leo needs to drive from Boston to Chicago. He planned to drive for 20 hours at an average speed of 50 mph. But drove 60 mph for the first 5 hours. During the remaining part of the trip, his average speed was 50 mph, how much earlier did he arrive in Chicago than he originally planned?

He arrived 1 hour earlier.

The formula for distance in this case is

d=rt, where d is distance, r is rate (speed) and t is time.

The first leg of his trip, he traveled at 60 mph for 5 hours:

d = 60 (5) = 300

He traveled 300 miles during the first part of his trip.

He had originally planned to travel 50 mph for 20 hours:

d = rt = 50 (20) = 1000

His entire trip is 1000 miles.

The second part of the trip is then represented by

1000-300 = 50t

700 = 50t

Divide both sides by 50:

700/50 = 50t/50

14 = t

He traveled 5 hours for the first part and 14 hours the second part, for a total of 19 hours.

This is 20-19 = 1 hour earlier than he'd planned.