So I'm trying to answer this question:
Every customer has an average of a purchase every 10 minutes. That equals 1/600 purchases per second.
My question is: How many customers do I need in order to have a 1% chance of having 30 purchases per second?
I think that I should use poisson here, but kind of like 'reverse' poisson where I know the P(X) and I need to find out the mean. After that I just divide the mean by 1/600 and I get the number of customers. Is that approach correct?