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    				| 1. | The probability that a driver must stop at any one traffic light is 0.2. There are 15 sets of traffic lights on the journey. (а) What is the probability that a student must stop at exactly 2 of the 15 sets of traffic lights? (b) What is the probability that a student will be stopped at 1 or more of the 15 sets of traffic lights? | 
| Answer» Let X be the binomial random variable denoting the number of traffic lights. Given n = 15, p =0.2, q = 0.8 (a) P(X = 2) = 15C2 (0.2)2 (0.8)13 = 105 (0.04) (0.8) [(0.8)4]3 = 0.2309 (b) P(X ≥ 1) = 1 - 9(X < 1) = 1 - P(X = 0) = 1 - 15C0 (0.2)0 (0.8)15 = 1 - (0.8)15 = 0.9648 | |