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Warm-Up • A sociologist studies social mobility in England by recording the social class of a large sample of fathers and their sons. The social classes are ordered from Class 1 (lowest) to Class 5 (highest). Here are the probabilities that the son of a lower class (Class 1) father will end up in each social class. • Let A be the event that the son remains in class 1 • Let B be the event that the son reaches one of the two highest classes. • Find the following probabilities • P(A) • P(B) • Probability that the son does NOT remain in class 1? P(Ac) • Probability that the son remains in the lower class or reaches one of the top two classes. P(A or B)
Homework Solutions #7-13 7. A. 0.04 B. 0.69 8. 0.54 9. 0.67 due to cardiovascular disease or cancer 0.33 due to other causes 10. A. 0.27 B. 0.73 11. A. 0.65 B. 0.38 C. 0.62 12. A. 1 B. 0.59 C. 0.64 13. Win a large battle 0.6 probability vs. 0.512 probability of winning three small battles
Multiplication rules work for compliments as well! • Look at example #15 • A string of Christmas lights contains 20 lights. The lights are wired in a series, so that if any light fails the whole string will go dark. Each light has a probability or 0.02 of failing during a 3-year period. The lights fail independently of each other. What is the probability that the string of lights will remain bright for 3 years?
What is the probability of each light not failing? • What is the probability of all 20 lights not failing?
Example • Most sample surveys use random digit dialing equipment to call residential telephone numbers at random. The telephone polling firm Zogby International reports that the probability that a call reaches a live person is 0.2. Calls are independent. • A polling firm places 5 calls. What is the probability that none of them reaches a person? • When calls are made to NYC, the probability of reaching a person is only 0.08. What is the probability that none of 5 calls made to NYC reaches a person?
Example (classwork) • The table below shows the probabilities of selecting a given color of M&Ms: • Does the table contain all colors? How do you know? • What is the probability of choosing and M&M of a different color than what is listed? • What is the probability of choosing an M&M that is brown or yellow? • If you choose 2 M&Ms at random, what is the probability that both are brown or yellow?