4.Z-INT: p1− p2.: Confidence interval for the difference of two proportions, p1-p2, for large samples with unknown population variances.

5.T-INT: 1 ∝.: Single sample confidence interval for the population mean, ∝, for small samples with unknown population variance.

6.T-INT: ∝1−∝2.: Confidence interval for the difference of the population means, ∝1- ∝2, for small samples with unknown population variances.

Example 1 – Determine the centered confidence interval for the mean of a population if a sample of 60 elements indicate that the mean value of the sample is x = 23.2, and its standard deviation is s = 5.2. Use α = 0.05. The confidence level is C = 1-α= 0.95.

Select case 1 from the menu shown above by pressing @@@OK@@@. Enter the values required in the input form as shown:

Press @HELP to obtain a screen explaining the meaning of the confidence interval in terms of random numbers generated by a calculator. To scroll down the resulting screen use the down-arrow key ˜. Press @@@OK@@@ when done with the help screen. This will return you to the screen shown above.

To calculate the confidence interval, press @@@OK@@@. The result shown in the calculator is:

Press @GRAPH to see a graphical display of the confidence interval information:

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