6. A random variable can be described as:

(a) a probability of an event.

(b) a variable whose value is a numerical outcome of a random phenomenon.

(c) the proportion of times an event occurs over a long run of repeated trials.

(d) All of the answer options are correct.

8. Which of the following is always true?

(a) P(not A) = 1 P(A).

(b) P(A or B) = P(A) + P(B) P(A and B).

(c) P(A and B) = P(A)+P(B)P(A or B).

9. Researchers have noted that children who learn to play a musical instrument through taking lessons have higher average SAT scores, higher average GPAs, and higher average class ranks. This is an example of:

(a) an experiment.

(b) an observational study.

(c) the establishing of a causal relationship through correlation.

(d) a block design, with music and nomusic groups as blocks.