Ex: A crate contains 10 light bulbs of which 4 are defective.
A Quality Control Inspector randomly samples 3 bulbs
without replacement. Let X = the number of defective bulbs
selected. Find the probability function, f(x), of the discrete
random variable X.
𝑓(𝑥 ) = 𝑃(𝑋 = 𝑥 ) =
6
(𝑥4)(3−𝑥
)
(10
)
3
Ex: An automatic camera records the number of cars running
a red light at an intersection (that is, the cars were going
through when the red light was against the car). Analysis of
the data shows that on average 15% of light changes record
a car running a red light. What is the probability that in 20
light changes there will be exactly three (3) cars running a
red light?