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m17 #33 Incorrect Ans?

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m17 #33 Incorrect Ans? [#permalink] New post 16 Oct 2011, 14:24
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Hello I think the answer to this question is incorrect.

Set S consists of positive numbers. If -1 is added as an element to set S, which of the following is impossible ?

The mean will decrease but median will not change.
The median will decrease but mean will not change.
The range will increase but median will not change.
The range will increase but mean will decrease.
The standard deviation will increase but mean will decrease.

Ans is given as B with the following explanation: Because -1 is smaller than any current element of set S, the mean of the set will definitely decrease if -1 is added to the set.

Should the answer be D?

Thanks.
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Re: m17 #33 Incorrect Ans? [#permalink] New post 16 Oct 2011, 15:37
martie11 wrote:
Hello I think the answer to this question is incorrect.

Set S consists of positive numbers. If -1 is added as an element to set S, which of the following is impossible ?

The mean will decrease but median will not change.
The median will decrease but mean will not change.
The range will increase but median will not change.
The range will increase but mean will decrease.
The standard deviation will increase but mean will decrease.

Ans is given as B with the following explanation: Because -1 is smaller than any current element of set S, the mean of the set will definitely decrease if -1 is added to the set.

Should the answer be D?

Thanks.


Correct. "D" should be the OA.

OA will be modified in the test.

thanks
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Re: m17 #33 Incorrect Ans? [#permalink] New post 17 Oct 2011, 00:13
martie11 wrote:
Hello I think the answer to this question is incorrect.

Set S consists of positive numbers. If -1 is added as an element to set S, which of the following is impossible ?

The mean will decrease but median will not change.
The median will decrease but mean will not change.
The range will increase but median will not change.
The range will increase but mean will decrease.
The standard deviation will increase but mean will decrease.

Ans is given as B with the following explanation: Because -1 is smaller than any current element of set S, the mean of the set will definitely decrease if -1 is added to the set.

Should the answer be D?

Thanks.


Subject: m17 #33 Incorrect Ans?

martie11 wrote:
Hello I think the answer to this question is incorrect.

Set S consists of positive numbers. If -1 is added as an element to set S, which of the following is impossible ?

The mean will decrease but median will not change.
The median will decrease but mean will not change.
The range will increase but median will not change.
The range will increase but mean will decrease.
The standard deviation will increase but mean will decrease.

Ans is given as B with the following explanation: Because -1 is smaller than any current element of set S, the mean of the set will definitely decrease if -1 is added to the set.

Should the answer be D?

Thanks.


I'm sorry martie/dzyubam. I didn't analyze the question properly: question says "IMPOSSIBLE", not MUST BE TRUE.

Answer is indeed "B".

The mean will decrease but median will not change.
{1,1,1}- Median=1, mean=1
{-1,1,1,1}-median=1; mean=0.5

The median will decrease but mean will not change.
NOT ENTIRELY POSSIBLE. ONLY PARTIALLY POSSIBLE. Median will decrease; mean also decreases. Median will remain unchanged; mean still decreases.

The range will increase but median will not change.
{1,1,1}- Median=1, range=0
{-1,1,1,1}-median=1; range=2

The range will increase but mean will decrease.
MUST BE TRUE Always.

The standard deviation will increase but mean will decrease.
Standard deviation may or may not increase. However, mean will always decrease. Possible.

Please ignore my earlier post.
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Re: m17 #33 Incorrect Ans? [#permalink] New post 18 Oct 2011, 21:00
@ fluke: Thanks for the explanation. I also got confused by the wordings of the statement.
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Re: m17 #33 Incorrect Ans? [#permalink] New post 25 Oct 2011, 04:41
ammulujnt wrote:
Ans D

The answer is in fact B...the question asks for what is "impossible"...I fell for the same trap.
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Re: m17 #33 Incorrect Ans? [#permalink] New post 28 Oct 2011, 16:39
B is Correct.

The median will decrease but mean will not change.

If you add a negative number to a positive numbers in Set S, the mean will definitely change (decrease!). So B is impossible.
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Re: m17 #33 Incorrect Ans? [#permalink] New post 17 Feb 2012, 19:45
Referring to fluke's post where he says -

"The standard deviation will increase but mean will decrease.
Standard deviation may or may not increase. However, mean will always decrease. Possible."

Why will Standard deviation may or may not increase? Why won't Std Dev. increase for sure if -1 is added?

Mean will decrease for sure always.
Re: m17 #33 Incorrect Ans?   [#permalink] 17 Feb 2012, 19:45
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