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# If a certain sample of data has a mean of 20 and a standard

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Senior Manager
Joined: 18 Jun 2007
Posts: 274
If a certain sample of data has a mean of 20 and a standard [#permalink]

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17 Oct 2008, 11:27
If a certain sample of data has a mean of 20 and a standard deviation of 3, which of the following values is more than 2.5 standard deviations from the mean?

A.12
B. 13.5
C. 17
D.23.5
E.26.5

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VP
Joined: 17 Jun 2008
Posts: 1477
Re: Standard Deviation [#permalink]

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17 Oct 2008, 12:13
mean +- 2.5 sd is from 12.5 to 27.5
Only number outside this range is 12. Hence, A.
Senior Manager
Joined: 18 Jun 2007
Posts: 274
Re: Standard Deviation [#permalink]

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18 Oct 2008, 13:52
Damn, I didn't get the wording right.
OA is A
VP
Joined: 17 Jun 2008
Posts: 1285
Re: Standard Deviation [#permalink]

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18 Oct 2008, 23:32
scthakur wrote:
mean +- 2.5 sd is from 12.5 to 27.5
Only number outside this range is 12. Hence, A.

I simply guessed through this question thought the value with max diff from mean is the answr

Can u tell me how u got the values 12.5 and 27.5
any calculations
_________________

cheers
Its Now Or Never

Senior Manager
Joined: 18 Jun 2007
Posts: 274
Re: Standard Deviation [#permalink]

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19 Oct 2008, 12:01
spriya wrote:
scthakur wrote:
mean +- 2.5 sd is from 12.5 to 27.5
Only number outside this range is 12. Hence, A.

I simply guessed through this question thought the value with max diff from mean is the answr

Can u tell me how u got the values 12.5 and 27.5
any calculations

spriya, read the question this way -->

If a certain sample of data has a mean of 20 and a standard deviation of 3, which of the following values is more than 2.5 (standard deviations) from the mean?

I hope now you will get how we get the answer
Senior Manager
Joined: 21 Apr 2008
Posts: 456
Schools: Kellogg, MIT, Michigan, Berkeley, Marshall, Mellon
Re: Standard Deviation [#permalink]

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19 Oct 2008, 12:12
spriya wrote:
scthakur wrote:
mean +- 2.5 sd is from 12.5 to 27.5
Only number outside this range is 12. Hence, A.

I simply guessed through this question thought the value with max diff from mean is the answr

Can u tell me how u got the values 12.5 and 27.5
any calculations

For me, it's easier think as follow:

the range is mean +- #SD. In this case, 20+-2.5*3. If you write 2.5 as 5/2, you get the range [25/2;55/2]

The only possible solution that is out of this range is A

CHeers

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Re: Standard Deviation   [#permalink] 19 Oct 2008, 12:12
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