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In the list of different positive numbers above, the arithmetic mean

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In the list of different positive numbers above, the arithmetic mean  [#permalink]

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New post 06 Jun 2017, 09:53
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A
B
C
D
E

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  65% (hard)

Question Stats:

53% (00:58) correct 47% (00:56) wrong based on 125 sessions

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a, b, c, d, e

In the list of different positive numbers above, the arithmetic mean is c. Which of the following changes to the list would necessarily increase the standard deviation?

A. Increase the value of b by 20%
B. Add the values (c + 3) and (c – 3) to the list
C. Add 10 to each value in the list
D. Multiply each value by -5
E. Divide each value by 2

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Re: In the list of different positive numbers above, the arithmetic mean  [#permalink]

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New post 07 Jun 2017, 11:18
luks like A...

B-- the two value c+3 and c-3 will shrink the SD because both add up the same value to average as c
C-- no change in SD
D-- SD goes down by 5%
E-- SD gets divided by 2..


must be A
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Re: In the list of different positive numbers above, the arithmetic mean  [#permalink]

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New post 07 Jun 2017, 11:27
1
2
Bunuel wrote:
a, b, c, d, e

In the list of different positive numbers above, the arithmetic mean is c. Which of the following changes to the list would necessarily increase the standard deviation?

A. Increase the value of b by 20%
B. Add the values (c + 3) and (c – 3) to the list
C. Add 10 to each value in the list
D. Multiply each value by -5
E. Divide each value by 2


Standard deviation INCREASES when the gap among values of the set increase.

A) Increase in value of b may not necessarily increase rather it may decrease the standard deviation if increased value of b becomes closer to mean
B) Adding these two values in list may decrease the standard deviation if it was already greater than 3
C) addition or subtraction of a constant in each element doesn't change the standard deviation as the deviation among terms remain constant
D) the gap among terms will also get multiplied by -5 and hence since deviation. Becomes 5 times so the standard deviation will definitely increase.

Answer Option D
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Re: In the list of different positive numbers above, the arithmetic mean  [#permalink]

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New post 09 Sep 2018, 06:47
GMATinsight wrote:
Bunuel wrote:
a, b, c, d, e

In the list of different positive numbers above, the arithmetic mean is c. Which of the following changes to the list would necessarily increase the standard deviation?

A. Increase the value of b by 20%
B. Add the values (c + 3) and (c – 3) to the list
C. Add 10 to each value in the list
D. Multiply each value by -5
E. Divide each value by 2


Standard deviation INCREASES when the gap among values of the set increase.

A) Increase in value of b may not necessarily increase rather it may decrease the standard deviation if increased value of b becomes closer to mean
B) Adding these two values in list may decrease the standard deviation if it was already greater than 3
C) addition or subtraction of a constant in each element doesn't change the standard deviation as the deviation among terms remain constant
D) the gap among terms will also get multiplied by -5 and hence since deviation. Becomes 5 times so the standard deviation will definitely increase.

Answer Option D



Hello GMATinsight, nice explanation :) could you please provide examples for all options if you dont mind ? :-)
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Re: In the list of different positive numbers above, the arithmetic mean &nbs [#permalink] 09 Sep 2018, 06:47
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