You have two testing methods A and B. Let X equal the measured values with method A and Y equal the measured values with method B. X and Y are both normally distributed and have a mean value of μ. Assume that the variance for X is $0.2^2$ and the variance for Y is $0.1^2$. Of the following suggestions, what is the best estimation for μ?
$$Y$$ $${{1}/{2}}X + {{1}/{2}}Y$$ $${{1}/{5}}X + {{4}/{5}}Y$$
I'm really stuck at this problem, so any help would be appreciated.