Give a simple example:

When buying lottery tickets, there is a 20% chance of winning 10, a 30% chance of winning 5, and a 50% chance of not winning.

What is the expectation of the money you can get?

Expected value = 20% *10+30% * 5+50% * 0 = 2+1.5+0 = 3.5, which means you can expect to get 3.5 yuan when you buy lottery tickets.

For a lottery ticket, you may not understand this 3.5, but if you buy/kloc-0.0 million lottery tickets and divide all the money in the lottery ticket by/kloc-0.0 million, the answer will be very close to 3.5, which is the meaning expressed by the expected value.

In other words, if the probability of all three cases is one-third, then the process of finding the expected value is the same as that of finding the average value.