The reporter randomly selected 10 people on the street, and the stem-and-leaf diagram of the number of spam text messages received within a month is as follows: (Ⅰ) Calculate the average number and sq

The reporter randomly selected 10 people on the street, and the stem-and-leaf diagram of the number of spam text messages received within a month is as follows: (Ⅰ) Calculate the average number and square of the sample

(Ⅰ) 17, (Ⅱ)

Test question analysis: (Ⅰ) Find the average first and then find its variance. The formula used is mean , variance . (II) Among 10 people, 2 people have less than 10 spam text messages. When 2 people are randomly selected, the value of the random variable is 0, 1, and 2. This probability is a classical concept, and the total number of basic events is . The basic number of events for a random variable is , and its probability can be calculated according to the classical probability formula, and then its distribution sequence and expectation can be obtained.

Test question analysis: Solution: (I) The average number of samples is . ?3 points

The variance of the sample is:?

(II) According to the meaning of the question, the random variable, , .

, ,

The distribution of random variables is

?. ?13 points