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According to a 2017 article in The Washington Post, \(72 \%\) of high school seniors have a driver's license. Suppose we take a random sample of 100 high school seniors and find the proportion who have a driver's license. Find the probability that more than \(75 \%\) of the sample has a driver's license. Begin by verifying that the conditions for the Central Limit Theorem for Sample Proportions have been met.

Short Answer

Expert verified
The probability that more than 75% of high school seniors have a driver’s license is approximately 0.2514 or 25.14%.

Step by step solution

01

Verify the conditions for the Central Limit Theorem for Sample Proportions

The conditions for the Central Limit Theorem conditions for sample proportions are: \n\n1. The sampling method is simple random sampling. It is stated in the problem that we are taking a random sample of 100 high school seniors, so this condition is met. 2. The samples are independent. Since the sample size of 100 is less than 10% of all high school seniors (assuming there are more than 1,000 high school seniors), we can assume independence. 3. There are at least 10 successes and failures in the population. Since 72% of the high school seniors have driver’s licenses, it means that at least 72 out of 100 succeeded in getting a drivers license, and at least 28 out of 100 do not have a driver’s license. Hence, this condition is satisfied.
02

Calculate the mean and standard deviation

The mean of the sample proportion is equal to the population proportion, which is 0.72. The standard deviation, denoted as σ, of a sampling distribution is calculated by: \[σ = \sqrt{ \frac{p(1-p)}{n}}\] where p is the population proportion and n is the sample size. Inserting the values, we get standard deviation as: \[σ = \sqrt{\frac{0.72(1 - 0.72)}{100}} = 0.045\]
03

Calculate the Z-score

The Z-score measures how many standard deviations an observation is away from the mean. Here, we need to calculate the Z-score for the sample proportion of 0.75 (75%), which is greater than the population mean. The Z-score is calculated by: \[Z = \frac{p - P}{σ}\] where p is the sample proportion, P is population proportion and σ is standard deviation of the sample. Inserting the values, we get Z-score as: \[Z = \frac{0.75 - 0.72}{0.045} = 0.67\]
04

Find the probability

We needed to find the probability that the poprortion is more than 0.75 (ie. \(P(p>0.75)\)), which can be found by finding the area to the right of the Z-score (0.67) using Z-table or any statistics software/tool. The area to the right of z-score 0.67 is \(0.2514\), so, the probability that more than 75% of the students have a driver’s license is around 0.2514 or 25.14%.

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Just the Boys Refer to Exercise \(7.77\) for information. This data set records results just for the boys. $$\begin{array}{|lcc|}\hline & \text { Preschool } & \text { No Preschool } \\\\\hline \text { Grad HS } & 16 & 21 \\\\\hline \text { No Grad HS } & 16 & 18 \\\\\hline\end{array}$$ a. Find and compare the percentages that graduated for each group, descriptively. Does this suggest that preschool was linked with a higher graduation rate? b. Verify that the conditions for a two-proportion confidence interval are satisfied. c. Indicate which one of the following statements is correct. i. The interval does not capture 0 , suggesting that it is plausible that the proportions are the same. ii. The interval does not capture 0 , suggesting that it is not plausible that the proportions are the same. iii. The interval captures 0 , suggesting that it is plausible that the population proportions are the same. iv. The interval captures 0 , suggesting that it is not plausible that the population proportions are the same. d. Would a \(99 \%\) confidence interval be wider or narrower?

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