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

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Senior Manager
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If a certain sample of data has a mean of 20 and a standard [#permalink]  17 Oct 2008, 10:27
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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Re: Standard Deviation [#permalink]  17 Oct 2008, 11:13
mean +- 2.5 sd is from 12.5 to 27.5
Only number outside this range is 12. Hence, A.
Senior Manager
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Re: Standard Deviation [#permalink]  18 Oct 2008, 12:52
Damn, I didn't get the wording right.
OA is A
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Re: Standard Deviation [#permalink]  18 Oct 2008, 22:32
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
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Re: Standard Deviation [#permalink]  19 Oct 2008, 11:01
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
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Re: Standard Deviation [#permalink]  19 Oct 2008, 11:12
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

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Re: Standard Deviation   [#permalink] 19 Oct 2008, 11:12
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