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