(a) is fine
Where the correlation equals .
(c) Here you need to standardize , by subtracting off its mean, which clearly is 0 and dividing by it's standard deviation.
and are random variables with standard deviation and . They are both distributed normally, with and correlation (they are not independent).
(a) Find the standard deviations of 3X.
Is this just 3(0.2) = 0.6?
(b) Find the standard deviation of X - Y
How do I do this is X and Y are not independent? What is the formula for dependent RVs?
(C) What is