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 thought a)mean is 200cm*10*0=0 but the answer is 200cm, the variance is 200cm*10*1.5 but the answer is 1.41.

Need help~Please explain what is the mean and variance for this questions