An interesting aspect of statistics is the behaviour of distributions as their parameters approach infinity. Under certain conditions, some distributions will converge towards another known distributions. The central limit theorem is an example of this, which states that for a given distribution: As the number of events in a sample increases, the mean of the sample will approach the true mean of the distribution. This site has some simulations that demonstrate this convergent behaviour for the binomial theorem.
To apply the normal approximation to a binomial distribution, the following conditions must be fulfilled: