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What is mathematical expectation?
Mathematical expectation is the probability of every possible result in the experiment multiplied by the sum of its results.

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