China Naming Network - Baby naming - The order of appearance is determined by drawing lots. Through the preliminary competition, five teams, A and B, were selected to participate in the competition.
The order of appearance is determined by drawing lots. Through the preliminary competition, five teams, A and B, were selected to participate in the competition.
(Ⅰ) ? (ii) The mathematical expectation of random variables is.
Test analysis: (1) Assuming that "Team A and Team B are just in the top two" is an event, then
So the probability that Team A and Team B are just in the top two is.
(ii) The possible values of a random variable are.
,
,
,
.
The distribution list of random variables is:
Because,
So the mathematical expectation of random variables is.
Comments: The key to calculating the probability of possible events such as this question is to list the basic event space correctly according to the meaning of the question and get the number of basic events it contains.