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is the standard deviation of number w,x,y,z greater than 2

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is the standard deviation of number w,x,y,z greater than 2 [#permalink] New post 10 Jun 2008, 22:07
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is the standard deviation of number w,x,y,z greater than 2
(1) w =3
(2) the average of four numbers is 8


analysing statement 1

value of x, y,z are not defined hence this statement is insufficent

analysing statement 2

we are given that average of 4 numbers is 8
but again we do not know the individual values for the variables w,x,y,z

therefore statement 2 is insufficent

together both statements put together
we get

w=3
average of four numbers is 8, but we still do not know the values of x,y and z

so we cant arrive at the standard deviation of these 4 numbers

IMO E should be the answer (which needless to say is different from what the OA is)

am i missing something in this question
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Re: DS question [#permalink] New post 10 Jun 2008, 22:34
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vdhawan1 wrote:
is the standard deviation of number w,x,y,z greater than 2
(1) w =3
(2) the average of four numbers is 8


analysing statement 1

value of x, y,z are not defined hence this statement is insufficent

analysing statement 2

we are given that average of 4 numbers is 8
but again we do not know the individual values for the variables w,x,y,z

therefore statement 2 is insufficent

together both statements put together
we get

w=3
average of four numbers is 8, but we still do not know the values of x,y and z

so we cant arrive at the standard deviation of these 4 numbers

IMO E should be the answer (which needless to say is different from what the OA is)

am i missing something in this question



ANS C .

1 and 2 alone not sufficient

if you combine both the statement: W=3 , now choose other three numbers closely clustered such that avg of W, X, Y,Z is 8 . Such data set is {3 , 9 , 9 ,10} , SD of which is > 2 , hence SD of any other combination will also be > 2 .
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Re: DS question [#permalink] New post 10 Jun 2008, 22:37
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standard deviation SD tell us how far / close numbers are from the mean.

if SD is low, means numbers are closer to mean.

Combinig the two statements, we have w = 3 and mean = 8.
Lets consider an example set where the numbers are closest to the mean, including w = 3. This set will be - 3,8,8,13.
now we can calculate SD for this set. It'll be sqrt((5^2+0^2+0^2+5^2)/4) = sqrt(12.5) which is more than 2.

Any other combination, SD will be more than this.

Answer is C.
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Re: DS question [#permalink] New post 10 Jun 2008, 22:56
durgesh79 wrote:
standard deviation SD tell us how far / close numbers are from the mean.

if SD is low, means numbers are closer to mean.

Combinig the two statements, we have w = 3 and mean = 8.
Lets consider an example set where the numbers are closest to the mean, including w = 3. This set will be - 3,8,8,13.
now we can calculate SD for this set. It'll be sqrt((5^2+0^2+0^2+5^2)/4) = sqrt(12.5) which is more than 2.

Any other combination, SD will be more than this.

Answer is C.



Ok guys got the point
thanks for the help
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The world is continuous, but the mind is discrete

Re: DS question   [#permalink] 10 Jun 2008, 22:56
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