6. Suppose that function f(x) = {6, otherwise x, 0xs is a probability density function of a continuous random variable X, then the variance Var(x) of X is 7. Assume that X is a binomial random variable, i.e. X-b(20,0.6), then the variance Var(2x)=_ 8. Assume that X is an exponential random variable with parameter 5, i.e. a probability density function is f(x) = S5e-5x, x > 0 0, X30 . Let a random variable Y = 5X – 5, then the correlation coefficient Pxy between X and Y is 9. Suppose that X ,X2, ..., Xn is a random sample from a population X~N(1,0%), where the mean u is unknown. Then, a confidence interval for the unknown parameter o2 with confidence level 1-a is 10. Suppose that X1, X2, ...,Xg is a random sample from a population X-N(0,1). Then, the distribution of the statistic X + X2 + ... +xz is