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# Can you solve this brainteaser?

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re: Can you solve this brainteaser?
3/1/2008 12:15:09 AM
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Hello everyone. No offense at first. It may not be such simple as we thought. What means a "brainteaser" ?

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re: Can you solve this brainteaser?
2/29/2008 5:11:46 PM
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When I first saw this, I was surprised that the answer is independent of the starting circumference. It's interesting that the answer is surprising, since I'm not surprised that circumference is proportional to radius. Maybe that means that the distributive property of multiplication is nonintuitive. I doubt the explanation is that simple, since another form of the question doesn't seem to be a riddle at all: A company pays each of its employees \$6.28 per hour, for a total of \$40,000 per hour. How much more would the company need to spend per hour to hire one more employee? C = 2*pi*R R' = R+1 C' = 2*pi*(R+1) = 2*pi*R + 2*pi = C + 2*pi Paul

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re: Can you solve this brainteaser?
2/28/2008 7:01:19 PM
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Try that again: The circumference is just over 40,000 km. I better give up :).

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re: Can you solve this brainteaser?
2/28/2008 7:00:01 PM
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on a completly different tangent: the string would stretch the extra approx. 2m as the requirement didn't specify tension to remain the same.

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re: Can you solve this brainteaser?
2/28/2008 6:59:28 PM
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Correction, I confused diameter with circumference. The diameter comes out to just over 40,000 km.

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re: Can you solve this brainteaser?
2/28/2008 5:27:47 PM
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I don't think any extra string is required. You already have 40,000 kilometers worth, which is way more than enough to encircle the earth.

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re: Can you solve this brainteaser?
2/28/2008 5:06:25 PM
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If string is lifted 1m, effective diameter increases by 2m. let d = 2meters. If D is original diameter then difference in circumference is C = (Pi*(D+d) - Pi*D) = Pi*d = 2*Pi meters = 6.283 meters

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re: Can you solve this brainteaser?
2/28/2008 2:41:52 PM
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If we assume a perfect circle of string then we can calculate the Diameter D C=Pi x D D=C/Pi = 40x10^6/Pi When you lift the string by 1 Meter, the diameter increases by 2 Meters. Then all you need to do is calculate the new circumference C and take the difference between old and new. NewC=(C/Pi + 2) x Pi To get the difference: Difference = NewC ? C = [(C/Pi + 2) x Pi ] ? C. = C + 2xPi ? C = 2xPi The answer I get is 2xPi Rick.

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re: Can you solve this brainteaser?
2/28/2008 12:32:12 PM
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It would be interresting how this equation looks, which gives the result how far we have to move to north or south... A real topic for my math teacher, who teased me with such questions back in school some decades ago.

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re: Can you solve this brainteaser?
2/28/2008 11:07:10 AM
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NO extra string needed to fill the gap if we could move our position towards southpole or northpole a little.

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