A newspaper finds that the mean number of typographical errors per page is fourfour. find the probability that (a) exactly fivefive typographical errors are found on a page, (b) at most fivefive typographical errors are found on a page, and (c) more than fivefive typographical errors are found on a page.
Accepted Solution
A:
For this question, we are given a mean/average rate, that is 4 errors per page; This suggests we need to use the Poisson distribution, so: Let X be the random variable, the number of errors per page; X~Po(4) ← X has a Poisson distribution with mean (λ) of 4 a) What we want is the probability that X = 5, so we use the formula for Poisson: [tex]P(X = 5) = \frac{e^{-(4)}. (4)^{5}}{5!}[/tex] = 0.156 (to 3 s.f.) b) What we want to find is the probability that X ≤ 5, so we have to use the cumulative tables: P(X ≤ 5) = 0.7851 c) What we want to find is the probability that X > 5, so we have to do a bit of manipulation and then use the cumulative tables; The tables give values for ≤, so we cannot directly look up a value for >, thus the manipulation: P(X > 5) = 1 - P(X ≤ 5) = 1 - (0.7581) = 0.2419