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Standard Deviation

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by winny » Tue Oct 11, 2011 10:01 am
What is the standard deviation of a given set of numbers whose average is 5?

1) None of the numbers are greater than their average.

2) The standard deviation is 5 when the value of each of the given numbers is increased by 7.

IMO it's D. Please correct me if I am wrong.

Statement (1) implies all the nos. must equal 5. Therefore, SD=0

Statement (2) adding the same no. to all the data points does not change the SD so the SD must be 5.
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Source: — Data Sufficiency |
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by sl750 » Tue Oct 11, 2011 10:19 am
Statement 1 is sufficient. If none of the numbers are greater than the average, which is 5. All the numbers in the set equal 5. SD=0

Statement 2 is also sufficient. Adding a constant to every element increases the average by the same amount. If the SD=5 in the new set, the old set has the same SD

What is interesting is that statement 2 contradicts statement 1
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by prodizy » Thu Oct 13, 2011 7:51 pm
Hey, this question doesn't make sense. How can we have a set with two different Standard Deviations? Both hints(A and B) are pointing to two different directions. This can't be a valid question.
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by GmatKiss » Sat Oct 15, 2011 7:26 am
IMO:D
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by sam2304 » Sat Oct 15, 2011 7:42 am
I agree with prodizy.

What is the OA ?

What is the standard deviation of a given set of numbers whose average is 5?

1.SD = 0
2.SD = 5

How are we supposed to answer with this ? It is E or the question is not valid
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by vaibhavgupta » Sat Oct 15, 2011 9:31 pm
winny wrote:What is the standard deviation of a given set of numbers whose average is 5?

1) None of the numbers are greater than their average.

2) The standard deviation is 5 when the value of each of the given numbers is increased by 7.

IMO it's D. Please correct me if I am wrong.

Statement (1) implies all the nos. must equal 5. Therefore, SD=0

Statement (2) adding the same no. to all the data points does not change the SD so the SD must be 5.
both give different values to SD ..

I think maybe the question is wrong.
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