Question

Suppose that only 25% of all drivers come to a complete stop at an intersection having flashing red lights
in all directions when no other cars are visible. What is the probability that, of 20 randomly chosen drivers
coming to an intersection under these conditions, at least 2 will come to a complete stop?

Answer 1

this is a binary problem ... s is stop , n is not stop

p(s) = .25 , p(n) = .75

(n + s)^20 = n^20 + 20 n^19 s + ... + 20 n s^19 + s^20

p(s ≥ 2) = 1 - [.75^20 + 20 (.75^19 * .25)]

Answer 2

74