Calculation formula:
1, discrete:
The values of discrete random variables X are X 1, X2, x3...xn, p(X 1), p(X2), p (x3)...p (xn), which is the probability of corresponding values of X, and can be understood as the appearance of data X1,X2, x3.
2, continuous type:
Let the probability density function of continuous random variable X be f(x), and if the integral is absolutely convergent, it is called the value of the integral.
Is the mathematical expectation of a random variable, expressed by E(X). that is
Examples of extended data:
10 products include 3 first-class products, 4 second-class products and 3 third-class products. Select 3 of these 10 products and find:
(1) The distribution table and mathematical expectation of the first-class product number X in the three products taken out;
(2) The probability that the number of first-class products is more than the number of second-class products in the three products taken out.
Solution:
The mathematical expectation of x e (x) = 0 * 7/24+1* 21/40+2 * 7/40+3 *1120 = 9/10.
Baidu Encyclopedia-Mathematical Expectation