15. A multiple choice quiz consists of 7 questions, each with 3 possible answers. If a student guesses at the answer to each question, then what is the mean number of correct answers?

16. What probability value would be needed to complete the following probability distribution?

x -5 -1 0 1 4

P(x) 0.12 0.24 0.12 0.24

17. If the possible values of a random variable X are between -1 and 6, is the mean of X positive or negative?

18. A researcher calculated the values and probabilities for a random variable X as shown below. Unfortunately, he erased the last value and needs to figure it out. If the mean of X was 2.2, then what was the last value?

x 0 1 3 ?

P(x) .4 .1 .2 .3

19. A researcher wished to conduct a survey of college students to study their opinion about the proposed change in smoking rules. The researcher asked a group of 20 students – 11 of them supported the change, 6 of them did not, and 3 had no opinion. This is not a binomial model because

20. Find the mean of the distribution shown.

x -3 -2 -1 0

P(x) 0.20 0.24 0.47 0.09