This document summarizes key concepts in probability, including: 1) Defining probability as a measure of how often an event occurs. Probability is calculated by adding the probabilities of simple events within the event. 2) Introducing concepts like experiments, events, sample spaces, unions, intersections, and complements of events. 3) Explaining conditional probability and the relationship between independent and dependent events. 4) Summarizing rules for calculating probabilities of unions, intersections, and complements of events.

1. Pertemuan 6 - 7 PROBABILITAS Hdi Nasbey, M.Si Jurusan Fisika Fakultas Matematika dan Ilmu Pemgetahuan Alam

28. Example 1 In a certain population, 10% of the people can be classified as being high risk for a heart attack. Three people are randomly selected from this population. What is the probability that exactly one of the three are high risk? Define H: high risk N: not high risk P(exactly one high risk) = P(HNN) + P(NHN) + P(NNH) = P(H)P(N)P(N) + P(N)P(H)P(N) + P(N)P(N)P(H) = (.1)(.9)(.9) + (.9)(.1)(.9) + (.9)(.9)(.1)= 3(.1)(.9) 2 = .243 01/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

29. Example 2 Suppose we have additional information in the previous example. We know that only 49% of the population are female. Also, of the female patients, 8% are high risk. A single person is selected at random. What is the probability that it is a high risk female? Define H: high risk F: female From the example, P(F) = .49 and P(H|F) = .08. Use the Multiplicative Rule: P(high risk female) = P(H  F) = P(F)P(H|F) =.49(.08) = .0392 01/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |

31. The Law of Total Probability A P(A) = P(A  S 1 ) + P(A  S 2 ) + … + P(A  S k ) = P(S 1 )P(A|S 1 ) + P(S 2 )P(A|S 2 ) + … + P(S k )P(A|S k ) 01/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | A  S k A  S 1 S 2…. S 1 S k

33. Example We know: P(F) = P(M) = P(H|F) = P(H|M) = From a previous example, we know that 49% of the population are female. Of the female patients, 8% are high risk for heart attack, while 12% of the male patients are high risk. A single person is selected at random and found to be high risk. What is the probability that it is a male? Define H: high risk F: female M: male .12 .08 .51 .49 01/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |