The normal is a good approximation to the binomial when n is greater than or equal to 10.

The number of observations n must be large enough, and the value of p so that both np and n(1 - p) are greater than or equal to 10. This is a rule ... n(1 - p) = 75. Since both of these numbers are greater than 10, the appropriate normal distribution will do a fairly good job of estimating binomialprobabilities. hope i help am sorry if i didnt