2008 October 4th, 07:53 PM
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#1 (permalink) |
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Eager!
Join Date: Sep 2008
Posts: 47
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Standard Deviation
500 recoreds have the distribution that is symmetric about the mean 10.If 68% of distribution lies within one standard devition of the mean and the deviation is 2, then atleast how many records are less than 12?
160 320 340 420 460 SPOILER: D |
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2008 October 4th, 08:28 PM
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#2 (permalink) |
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TestMagic Guru
 
Join Date: May 2006
Location: USA
Posts: 1,178
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answer is 420.
The SD distribution can be represented as 2%(3rd sd),14%(2ndsd),34%(1st sd) on each side of the mean. Since the mean is 10, and 68% i.e 34%+34% of the dist lies within sd=2, so the 1st sd=2 So the percentage of records which are less than 12 will be 2+14+34+34= 84%. 84% of 500=420.
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2008 October 4th, 08:38 PM
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#3 (permalink) |
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TestMagic Guru
Join Date: May 2008
Location: Bangladesh
Posts: 1,059
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Good solution by genius. I am just pictorially representing it:
......................(10-2).................10................(10+2)....... ..................... ........................<------ 34%-----*-----34%------> <------- -50%--------------------*------------------50%---------------> So, less than 12 is (50+34) or 84%. |
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2008 October 5th, 10:52 AM
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#4 (permalink) |
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Gone in 120 sec
Join Date: Mar 2008
Posts: 608
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Maku,
Why cant we put max 50% on right side of the mean. It will give us the least value and stays with in one SD. ......................(10-2).................10................(10+2)....... ..................... ........................ <------ 16%-----*-----50%------> <------- -50%--------------------*------------------50%---------------> why is that The SD distribution can be represented as 2%(3rd sd),14%(2ndsd),34%(1st sd) on each side of the mean? |
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