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Imagine a steel band snug to the Earth that encircles it entirely along the equator (about 25,000 miles around). You add 10 feet to the band to create a gap between the band and the Earth so that it is no longer snug. The gap is large enough:
a) For a person to crawl under 
b) For a mouse to scamper under 
c) To slip a pioece of paper under 
d) For a baterium to swim under 
To find the answer, we need to find the radii for two differentlysized circles. The smaller circle has a circumference of 25,000 miles, and the larger circle has a circumference of 25,000 + 10/5280 (25,000.0018939) miles.
We'll round off this larger circumference to 25,000.002 miles. Let's now find the radii for the two circles with the following formula:
Radius = Circumference/2 x pi
For our purposes, 3.14 is a good enough approximation for pi. So here goes:
Radius of Smaller Circle:
1) Radius = 25,000/2 x 3.14 
2) Radius = 25,000/6.28 
3) Radius = 3980.8917 miles, radius of the smaller circle 
Radius of Larger Circle
1) Radius = 25,000.002/2 x 3.14  
2) Radius = 25,000.002/6.28  
3) Radius = 3980.8920 miles, the radius of the larger circle.
The Answer!Subtract the smaller radius from the larger radius: 3980.8920  3980.8917 = 0.0003 miles. Because 0.0003 x 5,280 feet = 1.584 feet, the answer is a) large enough gap for a person to crawl under. A Simpler Way!My friend Roxana let me know of a much, much simpler way to solve the puzzle: Use this formula:
Finis
