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The Watchdog (Posted on 2004-10-28) Difficulty: 5 of 5
A watchdog is tied to the outside wall of a round building 20 feet in diameter. If the dog's chain is long enough to wind half way around the building, how large an area can the watchdog patrol?

See The Solution Submitted by Erik O.    
Rating: 3.4000 (5 votes)

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Give it a go | Comment 11 of 29 |
Unless I'm missing something, this is just a circle inside a circle problem.

Area of building (r = 10),  pi*r^2 = 100pi. C = piD = 20pi

Chain Area for Dog (r =  chain = 10pi), pi*r^2 = pi*(10pi)^2 = 100pi^3.

Patrol area = 100pi^3 - 100pi, assuming the dog can't get inside the house.

  Posted by bob909 on 2004-10-29 12:20:18
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