# Probability theory: Exponential distribution

This is part of the course “Probability Theory and Statistics for Programmers”.

**The exponential distribution** is the probability distribution that describes a process in which events occur continuously and independently at a constant average rate. This distribution is a continuous analog of the geometric distribution. With exponential distribution, we can find the probability of event occur before/after some moment of time. Lambda is the average number of events in one unit of time(hours, minutes, seconds, …).

Let’s take an example from the previous article, but now will find the different probability. Some pizzeria receives an average of 20 orders per hour. Find the probability that in just two minutes the pizzeria will receive an order.

As you can see from the chart probability that event will occur increasing with the time.

Let’s take a look at the characteristics of the Exponential distribution. The mean and the variance:

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