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 On The Edge (Posted on 2004-10-24)
Consider a round jar with no lid. The radius of the opening in the jar is 10. A coin (with a radius R < 10) can be placed flat on the edge of the jar without falling. The coin can be placed such that its center is on the rim of the jar, or it can be moved toward the center of the jar.

What is R, when the coin is as close to the center of the jar as possible without falling in, and the inside edge of the coin is at the center of the jar's opening?

 See The Solution Submitted by Brian Smith Rating: 3.0000 (6 votes)

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 Layman speak | Comment 5 of 7 |
the way i would approach this is to imagine a line through the centre of the coin, this line intersects the edge of the coin 180 degrees opposed.

now if both of these point are outside the rim of the jar and the centre is inside, then the coin will balance.

the trick is to find a coin that will balance like in the question when the jar is R10.

I do not have a clue where to go from here, sorry

 Posted by Juggler on 2004-10-24 16:50:09

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