Five distributions that cover most questions

A data science interviewer rarely names the distribution. They describe a business: "Orders reach a small online shop at about three an hour. What's the chance of a whole hour with no orders?" Much of the credit goes to the first sentence you say back, the one that names the distribution and the reason, before any formula. After this lesson you will be able to match a story to one of five distributions, state its mean and variance from memory, swap a slow exact calculation for a Poisson or normal approximation, and explain memorylessness in a sentence.

One small online shop runs through the whole lesson, because a single business produces every one of these distributions.

Pick the distribution from the story

Each distribution is a story about how the numbers were produced. Learn the story and the formulas come with it.