The Normal Probability Distribution
Definition:
If a continuous random variable has a probability distribution with a graph that is symmetric
and bell-shaped, and it can be described by the function equation
$$
f(x)=\frac{1}{\sigma\sqrt{2\pi}}e^{-\frac{1}{2}(\frac{x-\mu}{\sigma})^2} \quad\quad -\infty \leq x \leq \infty
$$
then we say it has a normal distribution.