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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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Most popular questions from this chapter

Bob Ross hosted a weekly television show, The Joy of Painting, on PBS in which he taught viewers how to paint. During each episode, he produced a complete painting while teaching viewers how they could produce a similar painting. Ross completed 30,000 paintings in his lifetime. Although it was an art instruction show, PBS estimated that only \(10 \%\) of viewers painted along with Ross during his show based on surveys of viewers. For each of the following, also identify the population and explain your choice. a. Is the number 30,000 a parameter or a statistic? b. Is the number \(10 \%\) a parameter or a statistic?

The Gallup poll reported that \(45 \%\) of Americans have tried marijuana. This was based on a survey of 1021 Americans and had a margin of error of plus or minus 5 percentage points with a \(95 \%\) level of confidence. a. State the survey results in confidence interval form and interpret the interval. b. If the Gallup Poll was to conduct 100 such surveys of 1021 Americans, how many of them would result in confidence intervals that did not include the true population proportion? c. Suppose a student wrote this interpretation of the interval: "We are \(95 \%\) confident that the percentage of Americans who have tried marijuana is between \(40 \%\) and \(50 \%\)." What, if anything, is incorrect in this interpretation?

A school district conducts a survey to determine whether voters favor passing a bond to fund school renovation projects. All registered voters are called. Of those called, \(15 \%\) answer the survey call. Of those who respond, \(62 \%\) say they favor passing the bond. Give a reason why the school district should be cautious about predicting that the bond will pass.

The 2017 Chapman University Survey of American Fears asked a random sample of 1207 adults Americans if they believed that aliens had come to Earth in modern times, and \(26 \%\) responded yes. a. What is the standard error for this estimate of the percentage of all Americans who believe that aliens have come to Earth in modern times? b. Find a \(95 \%\) confidence interval for the proportion of all Americans who believe that aliens have come to Earth in modern times. c. What is the margin of error for the \(95 \%\) confidence interval? d. A similar poll conducted in 2016 found that \(24.7 \%\) of Americans believed aliens have come to Earth in modern times. Based on your confidence interval, can you conclude that the proportion of Americans who believe this has increased since 2016 ?

From Formula \(7.2\), an estimate for margin of error for a \(95 \%\) confidence interval is \(m=2 \sqrt{\frac{\hat{p}(1-\hat{p})}{n}}\) where \(\mathrm{n}\) is the required sample size and \(\hat{p}\) is the sample proportion. Since we do not know a value for \(\hat{p}\), we use a conservative estimate of \(0.50\) for \(\hat{p}\). Replace \(\hat{p}\) with \(0.50\) in the formula and simplify.

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