Nr of people entering a store per min. is 3.8.

If 30 non-overlapping minutes are picked, then what is the probability that in at least 20 of these minutes, at least 4 people arrived to the store.

I've calculated for P(X>=4) , which was approximately 0.5265.

But how do you go on from here. Is it binomial now? Should I now approximate or use the central limit theorem or something?

Btw, answer to question is 0.09, but how to solve?