Posted by Ryan on Monday, July 8, 2013 at 11:39am.
In the Federal Trade Commission (FTC) \Price Check" study of electronic checkout scanners, the
FTC inspected 1,669 scanners at retail stores and supermarkets by scanning a sample of items at
each store and determining if the scanned price was accurate. The FTC gives a store a \passing
grade" if 98% or more of the items are priced accurately. Of the 1,669 stores in the study, 1,185
passed inspection.
a. Find a 90% con dence interval for the true proportion of retail stores and supermarkets with
electronic scanners that pass the FTC pricecheck test. Interpret your result.

Statistics  MathGuru, Monday, July 8, 2013 at 7:08pm
Use a confidence interval formula for proportions. Here's one example:
CI99 = p + or  (2.58)(sqrt of pq/n)
...where sqrt = square root, p = x/n, q = 1  p, and n = sample size.
Remember you need a 90% confidence interval; my example uses a 99% confidence interval. You will need to adjust accordingly.
Another hint: x = 1185, n = 1669
I hope this will help.
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