There are 2 ways that we can do this….
We can calculate out the probability for each event (245 show up, 5 do not) with the appropriate possibility…
0.98245 x 0.025 x 250!/245!/5! = ~17.742%
(Please note that I removed a description of the Poisson distribution, as it gives a number, but it is not exact. The Poisson probability would be 17.547%)