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Alex
3 years ago
11

There are 9,481 eligible voters in a precinct. 500 were selected at random and asked to indicate whether they planned to vote fo

r the Democratic incumbent or the Republican challenger. Of the 500 surveyed, 350 said they were going to vote for the Democratic incumbent. Using an 80% confidence level, what are the confidence limits for the proportion that plan to vote for the Democratic incumbent
Mathematics
1 answer:
maria [59]3 years ago
8 0

Answer:

The confidence limits for the proportion that plan to vote for the Democratic incumbent are 0.725 and 0.775.

Step-by-step explanation:

In a sample with a number n of people surveyed with a probability of a success of \pi, and a confidence level of 1-\alpha, we have the following confidence interval of proportions.

\pi \pm z\sqrt{\frac{\pi(1-\pi)}{n}}

In which

z is the zscore that has a pvalue of 1 - \frac{\alpha}{2}.

Of the 500 surveyed, 350 said they were going to vote for the Democratic incumbent.

This means that n = 500, \pi = \frac{350}{500} = 0.75

80% confidence level

So \alpha = 0.2, z is the value of Z that has a pvalue of 1 - \frac{0.2}{2} = 0.9, so Z = 1.28.

The lower limit of this interval is:

\pi - z\sqrt{\frac{\pi(1-\pi)}{n}} = 0.75 - 1.28\sqrt{\frac{0.75*0.25}{500}} = 0.725

The upper limit of this interval is:

\pi + z\sqrt{\frac{\pi(1-\pi)}{n}} = 0.75 + 1.28\sqrt{\frac{0.75*0.25}{500}} = 0.775

The confidence limits for the proportion that plan to vote for the Democratic incumbent are 0.725 and 0.775.

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