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# Statistics

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Senior Manager
Joined: 10 Nov 2010
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Statistics [#permalink]  03 Feb 2011, 09:03
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How many integers lie between the mean and the Standard deviation?

Given 25,30,35,40,45.
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Re: Statistics [#permalink]  03 Feb 2011, 09:24
Expert's post
GMATD11 wrote:
How many integers lie between the mean and the Standard deviation?

Given 25,30,35,40,45.

This is not a GMAT type of question plus it has very poor and ambiguous wording.

If the question is: how many of the 5 listed data points are within 1 standard deviation of the mean then the answer will be 3: mean=35 and SD=~7, so there are 3 data points from mean-SD=35-7=28 to mean+SD=35+7=42, namely: 30, 35, and 40.
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Re: Statistics [#permalink]  05 Feb 2011, 07:17
how do u calculate the sd?
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Re: Statistics [#permalink]  05 Feb 2011, 07:30
Hi Bunnel,

Is the SD not 5?
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Re: Statistics [#permalink]  05 Feb 2011, 07:43
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Expert's post
144144 wrote:
how do u calculate the sd?

Again: this is not a GMAT type of question, plus it has very poor and ambiguous wording. So, I wouldn't worry about it at all.

Anyway: you won't be asked to actually calculate the standard deviation of a set on the GMAT. You just need to understand the concept of it: standard deviation shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values.

Check this for more: math-standard-deviation-87905.html

CompetitiveAaron wrote:
Hi Bunnel,

Is the SD not 5?

No, $$SD=\sqrt{50}$$. check the above links for more.
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Re: Statistics [#permalink]  05 Feb 2011, 09:57
2
KUDOS
25,30,35,40,45.

mean = 25+45/2=70/2=35

$$\sigma^2 = \frac{(25-35)^2+(30-35)^2+(35-35)^2+(40-35)^2+(45-35)^2}{5}$$
$$\sigma^2 = \frac{100+25+0+25+100}{5}$$
$$\sigma^2 = \frac{250}{5}$$
$$\sigma^2 = 50$$
$$\sigma = \sqrt{50} \approx 7$$

where $$\sigma$$ is standard deviation.

How many integers in the dataset are within 1 std dev about the mean=35

Minimum= 35-7=28
Maximum= 35+7=42

Ans: 3 (30, 35 and 40)
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Re: Statistics [#permalink]  06 Feb 2011, 11:51
Thanks Bunuel and Fluke.. +1 kudos to you both
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Re: Statistics [#permalink]  06 Feb 2011, 13:09
Fluke - great work. +1
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Re: Statistics   [#permalink] 06 Feb 2011, 13:09
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