In the next preview assignment and in the next class, you will continue to use contingency tables to calculate probabilities and extend to the new concept of conditional probabilities.
Basic Probabilities
Question 1
If someone has a laptop, are they likely to own a desktop computer? If someone has a desktop computer, are they likely to own a laptop? Suppose a researcher conducts a survey of 120 randomly selected college students to try to answer these questions. The results of the survey are displayed in the following table.
| Owns laptop | Does not own
laptop |
Total | |
| Owns desktop | 20 | 20 | 40 |
| Does not own
desktop |
60 | 20 | 80 |
| Total | 80 | 40 | 120 |
- Calculate the probability that a student owns a laptop. Round to the nearest hundredth.
- Calculate the probability that a randomly selected student owns a desktop computer. Round to the nearest hundredth.
- Calculate the probability that a randomly selected student owns a desktop computer AND a laptop. Round to the nearest hundredth.
- Calculate the probability that a randomly selected student owns a desktop computer OR a laptop? Round to the nearest hundredth.
Conditional Probabilities
Question 2
Continue using the results of the previous study to answer the following questions.
- Calculate the probability that a randomly selected student owns a laptop GIVEN they own a desktop computer. Round to the nearest hundredth.
- Calculate the probability that a randomly selected student owns a desktop computer GIVEN they own a laptop. Round to the nearest hundredth.
- If a randomly selected student told you they own a desktop computer, would you guess they also own a laptop? Explain.
- If a randomly selected classmate told you they own a laptop, would you guess they also own a desktop computer? Explain.
