Chapter 8 Day 5 Homework Solutions 17. A) X = number of hard drives tested until the first defective B) .0266 C) table 18. On calculator 19. B) .3349 20. A) success = missed shot C) .7379 21. A) geometric; X = number of draws until red is chosen B) .2449; .8163; .1837 C) k = 26 B) .0655 Mean of Geometric Distribution The mean of a geometric distribution is found using the formula: 1 p where p is the probability of success Recall, the mean is also called the expected value! Example Aaron’s love potion works on 90% of women. What is the expected number of girls that it will take before the love potion fails? Example Suppose Roberto, a well-known major league baseball player finished last season with a .325 batting average. He wants to calculate the probability that he will get his first hit of the new season in his first at-bat.You define a success as getting a hit and define the random variable X = number of at-bats until Roberto gets his first hit. Roberto wants to know the expected number of at bats until he gets a hit. What would you tell him?