phân phối chuẩnnormal distribution

A normal distribution has a bell-shaped curve that is symmetric about $\mu$, so the mean, median, and mode all coincide at the peak. The parameter $\sigma$ controls how wide the bell is: a small $\sigma$ gives a tall, narrow curve, while a large $\sigma$ gives a flatter, more spread-out curve.

The empirical rule (68–95–99.7): about 68% of the data fall within $\mu \pm \sigma$, about 95% within $\mu \pm 2\sigma$, and about 99.7% within $\mu \pm 3\sigma$. Any normal distribution can be converted to the standard normal distribution $N(0,1)$ by standardizing with $z = (x - \mu)/\sigma$.