This problem is confusing me too.

In a length manuscript, it is discovered that only 13.5% of the pages contain no typing errors. If we assume that the number of errors per page is a random variable with a Poisson distribution, find the percentage of pages that have exactly one error.

I get two different answers depending upon which Poisson formula I use, and I have no idea which is correct (if either is, that is!!))

Please.....help?