Sum of random variables

blur

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Mar 16, 2014
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we use 2 metre tape for distance measurement and that the measurement error for the full tape length has 0 mean and variance 1.5cm^2. Find the mean and the variance if the total distance measured by 10 tape lengths in the following case
a) all the errors are uncorrelated b) all pairs of errors have correlation 0.1 c) the errors of consecutive measurements have correlation 0.1, but all other errors are uncorrelated.

I did question a) but my answer is wrong.
a) total mean = 200cm*10*0=0 but answer is 200cm variance= 200*10*1.5=3000 but the answer is 1.41cm

Please help
 
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