Re: Sample Questions of ISI ME I (Mathematics) 2010 Discussion

Posted by Amit Goyal on Apr 12, 2010; 8:24am
URL: http://discussion-forum.276.s1.nabble.com/Sample-Questions-of-ISI-ME-I-Mathematics-2010-Discussion-tp4850019p4888918.html

Hi Sonal, mistake is quoted in the following step
=var(x1/n)+var(x2/n)+.......+var(xn/n)+"2cov(x1/n,x2/n)+2cov(x2/n,x3/n)+....+2cov(xn/n,x1/n)"
according to what you wrote (as quoted) there will be n covariance type terms but thats not the case and there are (sq(n) - n)/2 such terms.
For example when n = 4 then we have (sq(n) - n)/2 = 6 terms and not 4. Here is the elaboration:
=var(x1/n)+var(x2/n)+var(x3/n)+var(x4/n)+2cov(x1/n,x2/n)+2cov(x1/n,x3/n)+2cov(x1/n,x4/n)+2cov(x2/n,x3/n)+2cov(x2/n,x4/n)+2cov(x3/n,x4/n)