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Two roommates went by car to a movie theater, which is 20 miles from their apartment. Due to heavy traffic, it took them 40 minutes to get there. What was their average speed in miles per hour?

A 30

Forty minutes is $3840_w48_h37.png$ of an hour. Because average speed is distance divided by time, divide 20 miles by $5729_w9_h37.png$ hour to obtain 30 mph. It’s worthwhile to note that 60 mph is a mile a minute. In this case, it took 40 minutes to go 20 miles, and this is half a mile a minute, so their average speed was 30 mph.