Your instructor will survey your class. Count the number of students in the class today.

• Raise your hand if you have any change in your pocket or purse. Record the number of raised hands.
• Raise your hand if you rode a bus within the past month. Record the number of raised hands.
• Raise your hand if you answered “yes” to BOTH of the first two questions. Record the number of raised hands.

Use the class data as estimates of the following probabilities. P(change) means the probability that a randomly chosen person in your class has change in their pocket or purse. P(bus) means the probability that a randomly chosen person in your class rode a bus within the last month and so on. Discuss your answers.

• Find P(change).
• Find P(bus).
• Find P(change AND bus). Find the probability that a randomly chosen student in your class has change in his/her pocket or purse and rode a bus within the last month.
• Find P(change|bus). Find the probability that a randomly chosen student has change given that he or she rode a bus within the last month. Count all the students that rode a bus. From the group of students who rode a bus, count those who have change. The probability is equal to those who have change and rode a bus divided by those who rode a bus.