# Normal Approximation

### Normal Approximation to the Binomial

If:

**n · p ≥ 5**

** n · (1 − p) ≥ 5**.

The binomial distribution** B(n, p)** can be approximated by the normal distribution:

#### Example

In a particular city, one in three families have a phone in their home. If 90 families are chosen at random, calculate the probability that at least 30 of them will have a phone.

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