Question

Manufacturers don’t like defective products because it can give their brands a bad reputation. However, no production line is perfect. One line is filling soda bottles that are supposed to contain 2 liters. Typically, 99% of these bottles are properly filled. In a quality control sample of 25 bottles, what is the probability that at least 23 are properly filled?

Answer 1

0.99804932311

Explanation:

We solve this using binomial probability

Binomial probability formula

= nCx × p^x × q^n - x

= n!/(n - x)! x!

Where n = Number of trials = 25 samples

x = Number of successes = 23

p = probability of success = 99% = 0.99

q = probability of failure = 1 - p

= 1 - 0.99

= 0.01

Hence,

p(at least 23 are properly filled) = p(X ≥ x)

= [25!/(25 - 23)! × 23! × 0.99^23 × 0.01^25 - 23 ]+ [25!/(25 - 24)! × 24! × 0.99^24 × 0.01^25 - 24 ]+ [25!/(25 - 25)! × 23! × 0.99^25 × 0.01^25 - 25]

= [300 × 0.99 ^23 × 0.01^2] + [25 × 0.99^24 × 0.01^1] + [1 × 0.99^25 + 0.01^0]

= 0.0238084285 + 0.1964195352 + 0.7778213594

= 0.99804932311