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Standard deviation of a set

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pkw209 Master | Next Rank: 500 Posts Default Avatar
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Standard deviation of a set

Post Mon May 03, 2010 2:13 pm
Is the standard deviation of the set of measurements x1, x2, x3....x20 less than 3?

A) The variance for the set of measurements is 4.

B) For each measurement, the difference between the mean and that measurement is 2.

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gmatmachoman Legendary Member Default Avatar
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Post Tue May 04, 2010 5:38 am
ajith wrote:
pkw209 wrote:
Is the standard deviation of the set of measurements x1, x2, x3....x20 less than 3?

A) The variance for the set of measurements is 4.

B) For each measurement, the difference between the mean and that measurement is 2.
Variance in this Example is if mean is m

(m-x1)^2+(m-x2)^2 ......+ (m-x20)^2)/20

Standard deviation is the square root of the variance.

a) Variance =4 ; SD = 2
b) Variance = (2^2+2^2.....+2^2)/20 = 2^2 = 4; SD = 2

A and B are independently sufficient! D
@ajith bhai,

I thought u r gone with the wind!! Bhai i was missing u ...as i had some doubts in set theory..luckily LR bhai chipped in and solved couple of them..

@LR thanks..

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ajith Legendary Member
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Post Tue May 04, 2010 2:51 am
pkw209 wrote:
Is the standard deviation of the set of measurements x1, x2, x3....x20 less than 3?

A) The variance for the set of measurements is 4.

B) For each measurement, the difference between the mean and that measurement is 2.
Variance in this Example is if mean is m

(m-x1)^2+(m-x2)^2 ......+ (m-x20)^2)/20

Standard deviation is the square root of the variance.

a) Variance =4 ; SD = 2
b) Variance = (2^2+2^2.....+2^2)/20 = 2^2 = 4; SD = 2

A and B are independently sufficient! D

_________________
Always borrow money from a pessimist, he doesn't expect to be paid back.

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liferocks Legendary Member Default Avatar
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Post Tue May 04, 2010 12:42 am
duongthang wrote:
pls, help

what is variance?
You can get a detail definition here http://en.wikipedia.org/wiki/Variance

in simple word for a series
x1,x2,x3.. if mean is x

variance =[(x-x1)^2+(x-x2)^2+(x-x3)^2]/3

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tanviet Legendary Member Default Avatar
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Post Tue May 04, 2010 12:36 am
pls, help

what is variance?

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liferocks Legendary Member Default Avatar
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Post Mon May 03, 2010 5:38 pm
variance of a set=average of square root of difference between the mean and that measurements

and standard deviation=square root of variance

since both conditions provides the variance either is sufficient

Hence ans D

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