Highway math #1: Keep 3 seconds behind

Question

“Keep us 3 seconds behind that car,” requests the driver. When the car ahead passes under a shadow, you say, “zero one thousand, one one thousand, two one thousand, three!” Your driver slows down a little and requests again. You wait for another shadow or a crack in the road. You count again, and your car crosses on the word “three”. You’ve done it! How far is your car from the one ahead? Your car is going 60 miles per hour

Answer 1

60 mph = 88 feet per second.

So the answer is

3 Sec * 88 feet per second = 264 feet. 

Estimation: Notice you could convert MPH to and from FPS in your head, by treating 88 FPS as 90 FPS. Then you can estimate

FPS = 90/60 MPH = 3/2 * MPH, and

MPH = 2/3 FPS.

These are only estimates, but they’re close.