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A manufacturer of plumbing fixtures has developed a new type of washer less faucet. Let \(p = P\) (a randomly selected faucet of this type will develop a leak within \(2\) years under normal use). The manufacturer has decided to proceed with production unless it can be determined that \(p\) is too large; the borderline acceptable value of \(p\) is specified as \(.10\). The manufacturer decides to subject \(n\) of these faucets to accelerated testing (approximating \(2\) years of normal use). With \(X = \) the number among the \(n\) faucets that leak before the test concludes, production will commence unless the observed X is too large. It is decided that if \(p = .10\), the probability of not proceeding should be at most \(.10\), whereas if \(p = .30\) the probability of proceeding should be at most \(.10\). Can \(n = 10\) be used? \(n = 20\)? \(n = 25\)? What are the actual error probabilities for the chosen n?

Short Answer

Expert verified

The value is \(n = 25\). The actual error probabilities are \(\begin{array}{l}\alpha = 0.0980\\\beta = 0.0905\end{array}\).

Step by step solution

01

Define p-value in hypothesis testing and binomial probability.

The null hypothesis states that the population mean is equal to the value mentioned in the claim. If the null hypothesis is the claim, then the alternative hypothesis states the opposite of the null hypothesis.

\(\begin{array}{l}{H_0}:p = 0\\{H_a}:p \ne 0\end{array}\)

The formula for the value of the test statistic is given by,\(z = \frac{{\hat p - {p_0}}}{{\sqrt {\frac{{{p_0}\left( {1 - {p_0}} \right)}}{n}} }}\).

The sample proportion is calculated by dividing the number of successes by the sample size. \(\hat p = \frac{x}{n}\)

The likelihood of exactly\(x\)successes on\(n\)repeated trials in an experiment with two alternative outcomes is known as binomial probability (commonly called a binomial experiment).

The binomial probability is\({}_n{C_x} \cdot {p^x} \cdot {(1 - p)^{n - x}}\)if the likelihood of success on an individual trial is\(p\).

The number of alternative combinations of \(x\) objects chosen from a set of \(n\) objects is indicated by \({}_n{C_x}\).

02

Test the appropriate hypothesis.

Let the given be: The probability of rejecting the null hypothesis is at most\(0.10\).

\(\alpha = 0.10\)

The probability of failing to reject the null hypothesis is at most\(0.10\).

\(\beta (0.30) = 0.10\)

The null hypothesis states that the population mean is equal to the value mentioned in the claim. If the null hypothesis is the claim, then the alternative hypothesis states the opposite of the null hypothesis.

\(\begin{array}{l}{H_0}:p = 0.10\\{H_a}:p > 0.10\end{array}\)

Using the normal probability table in the appendix, find the z-score corresponding to a probability of\(1 - \alpha = 0.90\)(Note: take the complement because the test is right-sided):

\(z = 1.28\)

The population mean (of the hypothesis) is increased by the product of the z-score and the standard deviation to get the sample mean:

\(\begin{aligned}{c}\hat p &= p + z\sqrt {\frac{{p(1 - p)}}{n}} \\ &= 0.10 + 1.28\sqrt {\frac{{0.10(1 - 0.10)}}{n}} \end{aligned}\)

Using the normal probability table in the appendix, find the z-score corresponding to a probability of\(\beta (0.30) = 0.10\)(Note: take the complement because the test is right-sided):

\(z = - 1.28\)

The population mean (of the hypothesis) is increased by the product of the z-score and the standard deviation to get the sample mean:

\(\begin{aligned}{c}\hat p &= p + z\sqrt {\frac{{p(1 - p)}}{n}} \\ &= 0.30 - 1.28\sqrt {\frac{{0.30(1 - 0.30)}}{n}} \end{aligned}\)

The both expressions must be equal to each other.

\(\begin{aligned}{c}0.10 + 1.28\sqrt {\frac{{0.10(1 - 0.10)}}{n}} &= 0.30 - 1.28\sqrt {\frac{{0.30(1 - 0.30)}}{n}} \\ - 0.20 + 1.28\sqrt {\frac{{0.10(1 - 0.10)}}{n}} &= - 1.28\sqrt {\frac{{0.30(1 - 0.30)}}{n}} \\ - 0.20 &= - 1.28\sqrt {\frac{{0.30(1 - 0.30)}}{n}} - 1.28\sqrt {\frac{{0.10(1 - 0.10)}}{n}} \end{aligned}\)

\(\begin{aligned}{c} - 0.20\sqrt n &= - 1.28\sqrt {0.30(1 - 0.30)} - 1.28\sqrt {0.10(1 - 0.10)} \\\sqrt n &= \frac{{1.28\sqrt {0.30(1 - 0.30)} + 1.28\sqrt {0.10(1 - 0.10)} }}{{0.20}}\\n &= {\left( {\frac{{1.28\sqrt {0.30(1 - 0.30)} + 1.28\sqrt {0.10(1 - 0.10)} }}{{0.20}}} \right)^2}\\ &\approx 24\end{aligned}\)

03

Determine the value of \(\alpha ,\beta \).

Let solve for \(\alpha \):

The highest possible probability is \(\alpha = P(X > 4) = 0.0980\).

Let solve for\(\beta \):

The highest possible probability is \(\begin{array}{c}\beta = P(X \le 4) = P(X = 0) + P(X = 1) + ... + P(X = 4)\\ = 0.0905\end{array}\).

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