TI-83 Instructions

Computing Normal Percentiles

*Z* is the standard normal
random variable.

*X* is a normal random variable
with mean μ and standard deviation σ.

**Find
c such that P(Z < c) = p.**

- Press 2
^{nd}DISTR. The DISTR menu title is highlighted. - Select invNorm, the item #3, or press
3 and skip the next step.
- Press ENTER. The phrase invNorm( appears in the
display.
- Enter the value of
*p*. This number must be between 0 and 1. - Press ).
- Press ENTER. The value of
*c*appears in the display.

- Compute 1 –
*p*. - Use the above procedure
to find
*c*such that*P*(*Z*<*c*) = 1 –*p*.

- Press 2
^{nd}DISTR. The DISTR menu title is highlighted. - Select invNorm, the item #3, or press
3 and skip the next step.
- Press ENTER. The phrase invNorm( appears in the
display.
- Enter the value of
*p*. - Press comma.
- Enter the value of
μ.
- Press comma.
- Enter the value of
σ.
- Press ).
- Press ENTER. The value of
*c*appears in the display.

**Find
c such that P(X > c) = p.**

- Compute 1 –
*p*. - Use the above procedure
to find
*c*such that*P*(*X*<*c*) = 1 –*p*.

- Compute 1 - α.
- Use the above procedure
to find
*c*such that*P*(*X*<*c*) = 1 – α. This value of*c*is*z*_{a}.