Final answer:
The number of typing errors made by a typist follows a Poisson distribution with an average of 3.5 errors per page. If there are four or more errors on a given page, the typist has made more errors than the average.
Step-by-step explanation:
The given question is about the Poisson distribution and its application in calculating the probability of certain events.
In this case, the number of typing errors made by a typist follows a Poisson distribution with an average of 3.5 errors per page.
If four or more errors appear on a given page, the typist can be considered to have made more errors than the average.