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cookies with SD

by ruplun » Fri May 06, 2011 9:01 pm
Brett discovers that 150 bags of his favorite cookie contain a total of 3750 cookies.He then det
ermines that the cookies in a bag are normally distributed with a stndard deviation of 15.When Brett goes to the store to buy a bag of his favorite cookies, how many of the 1200 bags in the store contain more than 30 cookies?
A.24
B.25
C.50
D.192
E.600
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by atulmangal » Fri May 06, 2011 11:27 pm
ruplun wrote:Brett discovers that 150 bags of his favorite cookie contain a total of 3750 cookies.He then det
ermines that the cookies in a bag are normally distributed with a stndard deviation of 15.When Brett goes to the store to buy a bag of his favorite cookies, how many of the 1200 bags in the store contain more than 30 cookies?
A.24
B.25
C.50
D.192
E.600
This seems out of syllabus question...is this an official question???
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by ruplun » Fri May 06, 2011 11:55 pm
its a part of syllabus....mean and sd are there in gmat
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by clock60 » Sat May 07, 2011 12:03 am
the mean number of cookies is 3750/150=25
and SD is 15. with prob 68,26% the number of cookies will fall in to the (25+15) and (25-15) i mean with in one SD
and at least 68,26/2=34% will contain more then 25 cookies.
0,34*1200=408.
only answer E makes sence here.
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by ruplun » Sat May 07, 2011 12:53 am
Can't understand this explanation..please can anyone explain in detail
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by atulmangal » Sat May 07, 2011 6:24 am
ruplun wrote:Can't understand this explanation..please can anyone explain in detail
Thats what i actually wanna tell u..i know standard deviation and mean etc is a part of syllabus but this extra piece of info regrading Standard deviation needed to solve this question is out of syllabus...here is one link where @Stuart suggests the same..

https://www.beatthegmat.com/standard-dev ... t8560.html
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