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Citrus2011 [14]
3 years ago
15

I want to take a survey of students at my university to find out what proportion like the new bus service on campus. I believe t

hat 75% of students like the service. How many students will I need to survey if I want to estimate, with 99% confidence, the true proportion to within 2%?
Mathematics
1 answer:
tatiyna3 years ago
4 0

Answer:

You will need to sample at least 3108 students.

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}.

In this problem, we have that:

\pi = 0.75

99% confidence level

So \alpha = 0.01, z is the value of Z that has a pvalue of 1 - \frac{0.01}{2} = 0.995, so Z = 2.575.

The margin of error is:

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

How many students will I need to survey if I want to estimate, with 99% confidence, the true proportion to within 2%?

You need a sample size of at least n.

n is found when M = 0.02. So

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

0.02 = 2.575\sqrt{\frac{0.75*0.25}{n}}

0.02\sqrt{n} = 1.115

\sqrt{n} = \frac{1.115}{0.02}

\sqrt{n} = 55.75

\sqrt{n}^{2} = (55.75)^{2}

n = 3108

You will need to sample at least 3108 students.

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