For binomial distribution (for example, there are k successes in n trials, the probability of each success is p, and the distribution table finds the mathematical expectation and variance), and EX=np, DX=np( 1-p).
N is the number of tests and p is the probability of success.
For geometric distribution (the probability of success in each test is p until the test is successful), there are EX= 1/P and dx = p 2/q.
And anything common in distribution lists.
DX=E(X)^2-(EX)^2。
In probability theory and mathematical statistics, mathematical expectation (or simply mean, or expectation) is the sum of the possible results multiplied by the results in each experiment, which is one of the most basic mathematical characteristics. It reflects the average value of random variables.
The application of mathematical expectation and variance formula in senior high school mathematics;
1) random stock trading.
Random stock picking is to pick a stock in the stock market with your eyes closed. Assuming that both the stop loss line and the take profit line are 10%, because it is random stock picking, the winning rate is equal to the loss rate, and because of stamp duty, commission and handling fee, the winning rate is equal to the loss rate.
2) Trend stock trading.
Trend stock trading is based on inertia theory, and the winning rate has a great relationship with experience. Basically, it can be assumed that the average winning rate is 60% and the odds are 40%. Trend investors generally follow the principle of making money and running when losing money, such as take profit 10% and stop loss of 50%. The mathematical expectation is EP = 60% * 10.