Z score is a representation in statistics of the amount of standard deviations data that is above or below the average. Calculating the z score by hand can be time-consuming and complicated, but it can be easily found using a sophisticated calculator like the TI-83. The TI-83 is a calculator equipped to perform many functions, including one named invNorm (p) that computes a z score value when cumulative probabilities are given.
Press the "2nd" button and then press the "VARS" button. Using the down arrow, scroll to 3:invNormal( and press "enter."
Input your known probability in decimal form and add a parenthesis. For example, if your probability is 80, then input .8. On the screen it would look like: invNorm(.8)
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Press "enter." This will give you the z score to four decimal places.