What is the difference between pk and P in the distribution table of random variable X?
If x is a discrete random variable, and its probability distribution is P(X=xk)=pk (k= 1, 2, …), then sum sum(PK) is called the mathematical expectation of random variable x, abbreviated as expect, and recorded as E(X). If x is a continuous random variable and its probability density is f(x), then the mathematical expectation of x is