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10 Jun 2008, 23:07
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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
(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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10 Jun 2008, 23:34
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vdhawan1
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 .
10 Jun 2008, 23:37
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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.
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.
