15. Let X1, X2, . . . , Xn represent a random sample from a Rayleigh distribution with pdf

a. It can be shown that E(X2)  2u. Use this fact to construct an unbiased estimator of u based on and use rules of expected value to show that it is unbiased).

b. Estimate u from the following measurements of blood plasma beta concentration (in pmol/L) for n  10 men.
16.88 10.23 4.59 6.66 13.68 14.23 19.87 9.40 6.51 10.95