**1. Can a normal distribution not be symmetrical?**

Few distributions would be perfectly symmetrical. Often a distribution will be

skewed,which means it "leans" one way.In many cases, the larger the sample the nearer the curve comes to being a normal shape.

**2. Are all distributions normal?**

No! There are rectangular distributions, bi-modal distributions, triangular distributions...

**2. Why are there no tables for negative values of z?**

Because of the symmetrical nature of the normal curve the probabilities associated with the left hand side of the curve are the same so they are not repeated.