296 Chapter 7 The Normal Distribution Finding a z-score corresponding to a given area The invNorm command is used to calculate the z-score corresponding to an area to the left. Step 1. Press 2nd, then VARS to access the DISTR menu. Select 3:invNorm (Figure E). Step 2. Enter the area to the left of the desired z-score, comma, the mean (0 for the standard normal), comma, and the standard deviation (1 for the standard normal). Step 3. Press ENTER. Using the TI-84 PLUS Stat Wizards (see Appendix B for more information) Step 1. Press 2nd, then VARS to access the DISTR menu. Select 3:invNorm (Figure E). Step 2. Enter the area to the left of the desired z-score in the area field, the mean in the �� field (0 for the standard normal), and the standard deviation in the �� field (1 for the standard normal). Step 3. Select Paste and press ENTER to paste the command to the home screen. Press ENTER again to run the command. Figure F illustrates finding the z-score that has an area of 0.26 to its left (Example 7.8). Figure E Figure F MINITAB Finding areas under the standard normal curve The following procedure computes the area to the left of a given value. Step 1. Click Calc, then Probability Distributions, then Normal. Step 2. Select the Cumulative probability option. Step 3. Enter the value for the mean in the Mean field (0 for the standard normal) and the value for the standard deviation in the Standard deviation field (1 for the standard normal). Step 4. To compute the area to the left of a given x, enter the value for x in the Input constant field. Step 5. Click OK. Figures G and H illustrate finding the area to the left of z = 1.26 (Example 7.2). Figure G Figure H Finding a z-score corresponding to a given area The following procedure is used to calculate the z-score corresponding to an area to the left. Step 1. Click Calc, then Probability Distributions, then Normal. Step 2. Select the Inverse Cumulative Probability option. Step 3. Enter the value for the mean in the Mean field (0 for the standard normal) and the value for the standard deviation in the Standard deviation field (1 for the standard normal). Step 4. Enter the area to the left of the desired z-score in the Input constant field and click OK. Figure I illustrates finding the z-score that has an area of 0.26 to its left (Example 7.8). Figure I
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