is a binomial random variable
If the size
is adequately large,
then the distribution of
can be approximated by the normal distribution with
and standard deviation
That is, a normal distribution approximates a binomial distribution.
A general rule for ``adequately large''
Let be a normal random variable whose distribution approximates
the binomial distribution of a random variable .
Then the probability involving can be approximated by that of .
Having taken into account the fact that is a continuous random variable,
the approximated probability
is calculated with continuity correction.