Calculating a Confidence Interval for Proportions

Find the 95% confidence interval for the p when X = 60 and n = 500.

Press STAT, then RIGHT ARROW twice to TESTS. Press A to select A:1-PropZInt.

 
 
 

Enter 60 for x:. ARROW DOWN once and enter 500 for n:. ARROW DOWN once again to C-LEVEL:. Enter the confidence interval as the decimal .95. Then ARROW DOWN once more to Calculate and press ENTER. The results are shown below.

 
 

The final screen reports not only the confidence interval of the proportion p as (0.09152, 0.14848) in interval notation, but also is also given as 0.12.
This can also be written as 0.09152 < p < 0.14848.



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