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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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Most popular questions from this chapter

The article 鈥淯ncertainty Estimation in Railway Track Life-Cycle Cost鈥 (J. of Rail and Rapid Transit, 2009) presented the following data on time to repair (min) a rail break in the high rail on a curved track of a certain railway line.

\(159 120 480 149 270 547 340 43 228 202 240 218\)

A normal probability plot of the data shows a reasonably linear pattern, so it is plausible that the population distribution of repair time is at least approximately normal. The sample mean and standard deviation are \(249.7\) and \(145.1\), respectively.

a. Is there compelling evidence for concluding that true average repair time exceeds \(200\) min? Carry out a test of hypotheses using a significance level of \(.05\).

b. Using \(\sigma = 150\), what is the type II error probability of the test used in (a) when true average repair time is actually \(300\) min? That is, what is \(\beta (300)\)?

A new design for the braking system on a certain type of car has been proposed. For the current system, the true average braking distance at 40 mph under specified conditions is known to be 120 ft. It is proposed that the new design be implemented only if sample data strongly indicates a reduction in true average braking distance for the new design.

a.Define the parameter of interest and state the relevant hypotheses.

b.Suppose braking distance for the new system is normally distributed with 蟽= 10. Let \(\overline X \) denote the sample average braking distance for a random sample of 36 observations. Which values of \(\overline x \) are more contradictory to H0 than 117.2, what is the P-value in this case, and what conclusion is appropriate if 伪 = .10?

c.What is the probability that the new design is not implemented when its true average braking distance is actually 115 ft and the test from part (b) is used?

Pairs of P-values and significance levels, 伪, are given.

For each pair, state whether the observed P-value would lead to rejection of H0 at the given significance level.

a.P颅-value = .084, 伪= .05

b.P颅-value = .003, 伪= .001

c.P-颅value = .498, 伪= .05

d.P-颅value = .084, 伪= .10

e.P-颅value = .039, 伪= .01

f.P-颅value = .218, 伪 = .10

Each of a group of \(20\) intermediate tennis players is given two rackets, one having nylon strings and the other synthetic gut strings. After several weeks of playing with the two rackets, each player will be asked to state a preference for one of the two types of strings. Let \(p\) denote the proportion of all such players who would prefer gut to nylon, and let \(X\) be the number of players in the sample who prefer gut. Because gut strings are more expensive, consider the null hypothesis that at most \(50\% \) of all such players prefer gut. We simplify this to \({H_0}:p = .5\), planning to reject \({H_0}\) only if sample evidence strongly favors gut strings.

a. Is a significance level of exactly \(.05\) achievable? If not, what is the largest a smaller than \(.05\) that is achievable?

b. If \(60\% \) of all enthusiasts prefer gut, calculate the probability of a type II error using the significance level from part (a). Repeat if 80% of all enthusiasts prefer gut.

c. If \(13\) out of the \(20\) players prefer gut, should \({H_0}\) be rejected using the significance level of (a)?

The desired percentage of SiO2 in a certain type of aluminous cement is 5.5. To test whether the true average percentage is 5.5 for a particular production facility, 16 independently obtained samples are analyzed. Suppose that the percentage of SiO颅2 in a sample is normally distributed with

蟽 =3 and that \(\overline x = 5.25\).

a.Does this indicate conclusively that the true average percentage differs from 5.5?

b.If the true average percentage is 碌 = 5.6 and a level 伪 = .01 test based on n=16 is used, what is the probability of detecting this departure from H0?

c.What value of n is required to satisfy 伪 = .01 and 尾( 5.6)= .01?

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