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# Qa - correlation

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 priya Student [ Scorecard : 64] Posted On 26 May 2012 at 15:34 For two variables x and y , it is known that the cov(x,y) = 80, the variance of x is 16 and the sum of squares of deviation of y from its mean is 250. The number of observations for this bivariate data is a) 7            b) 8            c) 9                   d) 10 Thanks in advance. Tejaswi Kasturi student-cpt [ Scorecard : 402] Posted On 26 May 2012 at 15:56 we will try to solve the problem by exploiting the fact that correlations is always less than or equal to 1 correlation = 80/((standard deviation of x)*(stadard deviation of y)) standard deviation of x = squareroot(16) = 4 standard deviation of y = squareroot (250/N) = 5(10/N)^0.5 so we get 80/(4*5*(10/N)^0.5)  <1 implies 4 < (10/n)^0.5 implies 16 <10/N implies N<10/16 which is impossible. the figures do not make sense once again. even if they do we cannot find out N just with the help of covariance. Total thanks : 1 times intermediate(ipc)course no [ Scorecard : 1446] Posted On 26 May 2012 at 20:18 variance of y how much ??/ Tejaswi Kasturi student-cpt [ Scorecard : 402] Posted On 26 May 2012 at 23:03 we don't know because we were given only covariance and variance of x we could calculate it if we had correlation priya Student [ Scorecard : 64] Posted On 28 May 2012 at 14:49 Thanks.

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