90 mph is wrong. So is 72 mph. Or any other answer.....

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To average 60 mph (1 mile/min.), you must drive two laps (2 miles) in 2 minutes.

Lap 1 at 30 mph (2 mins/mile) takes you two minutes. Therefore, to average 60 Mph, you must finish the second lap in 0 minutes.

(So you cant do it unless you travel at infinite speed.)

[aside, for information only]

If we drive 90mph in the second lap, 90mph = 1.5 miles per minute. So itll take 40 seconds to do the lap.

You would have taken a total of 2 minutes, 40 seconds to do both laps.

2:40 = 160 seconds. Divide by 2 and thats 80 seconds per lap.

Therefore:

One mile in 80 seconds = ave. speed (over both laps) of 45 MPH. (not 60mph)

[/side, for information only]