Software Risk Assessment- Probability

Question 1: Suppose you have to determine the probability of each of the following three events: ï‚· England win the next FIFA World Cup ï‚· The first baby born in California on the 1 January next year will be a boy ï‚· OJ Simpson murdered his wife In each case explain whether you can meaningfully assign a subjective probability in each case and give reasons for doing, or not doing, so. [5 marks] Question 2: Consider an experiment in which two fair dice are thrown. A: `the sum of the dice is greater than or equal to 7′ B: `the second die is a 3′ C: `the difference between the dice is less than or equal to 2’. Calculate the respective probabilities of these events: 1. P(A) 2. P(B) 3. P(C) 4. P(AB) 5. P(AB) 6. P(BC) 7. P(BC) Make clear any assumptions you are making. Answers derived solely by means of enumeration will be penalised. [35 marks] Hints: Try enumerating over all possible events for the two dice and deriving probabilities for these. Also be careful about independence assumptions. Question 3: It is known that there is a single terrorist in a room of 100 people. A lie detection machine, which is 95% accurate, is used to identify the terrorist. What is the chance that the correct person is identified? Make clear any assumptions you use to come up with a solution. [10 marks]