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Question
NARRBEGIN: SA_108_112The following values have been calculated using the TDIST and TINV functions in Excel. These values come from a t- distribution with 15 degrees of freedom.
These values represent the probability to the right of the given positive values.
| Value | t -probability |
| 1.00 | 0.1666 |
| 1.20 | 0.1244 |
| 1.40 | 0.0909 |
| Probability | t -value |
| 0.20 | 1.3406 |
| 0.10 | 1.7531 |
| 0.05 | 2.1315 |
In past years, approximately 25% of all U.S. families purchased potato chips at least once a month. We are interested in determining the fraction of all U.S. families that currently purchase potato chips at least once a month. How many families must we survey if we want to be 99% sure that our estimate of the fraction of U.S. families currently purchasing potato chips at least once a month is accurate within 2%?
Answer
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