In the CASA teen survey described in the previous exercise, 33% of teens reported that parents are never present at parties they attend. Thirty-one percent of teens who say parents are never present during parties report that marijuana is available at the parties they attend, compared to only 1% of teens who say parents are present at parties reporting that marijuana is available at the parties they attend.
a. Which of these percentages estimates a conditional probability? For each that does, identify the event conditioned on and the event to which the probability refers.
b. For the variables parents present (yes or no) and marijuana available (yes or no), construct a contingency table showing counts for the 1297 teenagers surveyed.
c. Using the contingency table, given that marijuana is not available at the party, estimate the probability that parents are present.