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) = 15C(0.2)(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 - 15C(0.2)(0.8)15

= 1 - (0.8)15 = 0.9648



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