E(X) =｛45+50+49+52+47+50+42+53｝/8 = 388/8 = 48.5E{[X-E(X)]^2} = {(-3.5)²+1.5²+0.5²+3.5²+(-1.5)²+1.5²+(-6.5)²+4.5²+0²}/8 = 94/8 = 11.75方差： D(X) = 11.75
