Classifying Events Based on Studies In Exercises 15-18, identify the two events described in the study. Do the results indicate that the events are independent or dependent? Explain your reasoning. 15. A study found that people who suffer from moderate to severe sleep apnea are at increased risk of having high blood pressure. (Source: Journal of the American Medical Association) 16. Stress causes the body to produce higher amounts of acid, which can irritate already existing ulcers. But, stress does not cause stomach ulcers. (Source: Baylor College of Medicine) 17. A study found that there is no relationship between being around cell phones and developing cancer. (Source: British Medical Journal) 18. According to researchers, infection with dengue virus makes mosquitoes hungrier than usual. (Source: PLoS Pathogens) 19. Cards Two cards are selected from a standard deck of 52 playing cards. The first card is replaced before the second card is selected. Find the probability of selecting a heart and then selecting an ace. 20. Coin and Die A coin is tossed and a die is rolled. Find the probability of tossing a tail and then rolling a number greater than 2.