Statistics problems, like those that require you to calculate z-scores, can be computed much faster on a TI-84 calculator than using the normal distribution tables found in most statistics text books. With the TI-84 you can calculate the z-score with the "invNorm" function. This function requires that you enter the area to the left of the normal distribution curve that you want to calculate the z-score for. Calculating the z-score however does require that you access the TI-84's statistics "distribution" menu. This requires that you press the "2nd" key and then the "Vars" key.

Press and release the "On" key (column 1, row 10) on your TI-84's keypad to turn on your calculator.

Press and release the "2nd" key (column 1, row 2, yellow or orange key). Press and release the "VARS" key (column 4, row 4) to display the "distribution" menu on the TI-84's screen.

Press and release the "3" key (column 3, row 9) to select and display the "invNorm" function.

Use an area of 0.9 for the area parameter that the invNorm function requires. Press and release the "period" key (column 3, row 10). Press and release the "9" key (column 4, row 7). Check that you have typed in the correct number sequence and that the display now reads "invNorm(0.9".

Press and release the "Enter" key (column 5, row 10) to display the z-score for the area to the left of 0.9. Check that the z-score calculated and displayed on the TI-84 screen is "1.28."

#### Tip

If you need to calculate the z-score for the area to the right of the normal distribution, subtract the area to the left of the z-score from 1. To find the z-score to the area to the right of the normal distribution for an area of 0.9 enter in the invNorm function as "invNorm(1-0.9."

#### Warning

The area under the entire normal distribution curve is equal to one(1). This means that all values entered in the area parameter of the "invNorm" function must be between zero(0) and one(1). If you type in any other value, such as 10, the TI-84 will display a syntax error. Don't close the invNorm function with a closing parenthesis before you press the "Enter" key. A syntax error will occur.

#### Tips and warnings

- If you need to calculate the z-score for the area to the right of the normal distribution, subtract the area to the left of the z-score from 1. To find the z-score to the area to the right of the normal distribution for an area of 0.9 enter in the invNorm function as "invNorm(1-0.9."
- The area under the entire normal distribution curve is equal to one(1). This means that all values entered in the area parameter of the "invNorm" function must be between zero(0) and one(1). If you type in any other value, such as 10, the TI-84 will display a syntax error. Don't close the invNorm function with a closing parenthesis before you press the "Enter" key. A syntax error will occur.