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iragen [17]
3 years ago
12

As a manager for an advertising company, you must plan a campaign designed to increase Twitter usage. A recent survey suggests t

hat 85% of adults know what Twitter is. How many adults should you survey in order to be 90% confident that your estimate is within 5% of the true population proportion?
Mathematics
1 answer:
kolbaska11 [484]3 years ago
3 0
Given:
Sample proportion = 85% = 0.85.
Confidence level (CL) = 90%.
Confidence interval (CI) \hat{p} \pm z^{*} \sqrt{ \frac{\hat{p}(1-\hat{p})}{n} }  \\ where \\ n=sample\, size \\ z^{*}=1.645 \, at \, 90\% \, CL

We want the confidence interval to be 5% or 0.05. Therefore
0.85 - 1.645 \sqrt{ \frac{0.85(1-0.85)}{n} }=0.05 \\ 0.85 -  \frac{0.5874}{ \sqrt{n} } =0.05 \\  \frac{0.5874}{ \sqrt{n} }=0.8 \\  \sqrt{n} = .7342 \\ n=0.54

Because this number is less than 1, a default sample size of 30 (for the normal distribution) is recommended.

Answer: 30

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