# Statistics Guide: A normal population has a mean of 19 and a standard deviation of 5.

In this tutorial, we are going to use excel to calculate a z value from a know mean and standard deviation.

**Student Question:** A normal population has a mean of 19 and a standard deviation of 5.

### Compute the z value associated with 25

To find the z-value at 25, we calculate (25 – mean) / standard deviation =(25-19)/5

**Result: 1.20**

### What proportion of the population is between 19 and 25?

Finding the proportion between 19 and 25 can be found with the NORMDIST function in excel, then subtracting the result from 0.5.

=(NORMDIST(25,C2,C3, TRUE))-0.5

**Result: 0.38493**

### What proportion of the population is less than 17?

You can use the same function here, just don’t subtract the result from 0.5.

=NORMDIST(17,C2,C3,TRUE)

**Result: 0.34458**

**Student:**Brandy Golden**Textbook:**Business Statistics**Course:**QNT 351