Conditional Probability: Questions & Answers

Conditional Probability: Questions & Answers A box contains four red balls and eight black balls. Two balls are randomly chosen from the box, and are not replaced. Let event B be choosing a black ball first and event R be choosing a red ball second. What are the following probabilities? P(B)= P(R | B)= P(B n R)= The probability that the first ball chosen is black and the second ball chosen is red is about ______% - ANSWER: 8/12 4/11 8/33 24% A dentist polls his patients and finds that 83 percent brush their teeth at least twice a day, 47 percent floss daily, and 19 percent brush at least twice a day and floss daily. What is the probability that a patient flosses daily, given that he or she brushes at least twice a day? Round to the nearest percent. - ANSWER: B: 23% At a hospital, 56 percent of the babies born are not girls. Of the baby girls born, 12 percent are premature. What is the probability of a premature baby girl being born at this hospital? Round to the nearest percent. - ANSWER: 5%.....................................................