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Lightbulbs of a certain type are advertised as having an average lifetime of 750 hours. The price of these bulbs is very favorable, so a potential customer has decided to go ahead with a purchase arrangement unless it can be conclusively demonstrated that the true average lifetime is smaller than what is advertised. A random sample of 50 bulbs was selected, the lifetime of each bulb determined, and the appropriate hypotheses were tested using Minitab, resulting in the accompanying output.

Variable N Mean StDev SE Mean Z P-Value

Lifetime 50 738.44 38.20 5.40 -2.14 0.016

What conclusion would be appropriate for a significance level of .05? A significance level of .01? What significance level and conclusion would you recommend?

Short Answer

Expert verified

For significance level of\(0.05\)reject the null hypothesis.

For significance level of \(0.01\) do not reject the null hypothesis

Step by step solution

01

Step 1:Null hypothesis

The null hypothesis, denoted by H0, is the claim that is initially assumed to be true (the 鈥減rior belief鈥 claim). The alternative hypothesis, denoted by Ha, is the assertion that is contradictory to H0.

The null hypothesis will be rejected in favour of the alternative hypothesis only if sample evidence suggests that H0 is false. If the sample does not strongly contradict H0, we will continue to believe in the plausibility of the null hypothesis. The two possible conclusions from a hypothesis-testing analysis are then reject H0 or fail to reject H0.

02

Hypothesis is reject or not.

The interest of the potential customer is hypothesis \({H_0}:\mu = 750\) versus \({H_a}:\mu < 750\). At the significance level of \(0.05\) it can be concluded that the null hypothesis is to be reject. This is because the null hypothesis is rejected when \(z < - {z_\alpha }\). Since,

\(\begin{array}{l}{z_\alpha } = {z_{0.05}}\\ = 1.645\end{array}\)

And \(z = - 2.14\).

\(z < - {z_\alpha }\), the null hypothesis is rejected and the customer does not continue with the purchase.

However, at significance level of \(0.01\) the null hypothesis is not reject and the customers continue with the purchase. Since,

\({z_\alpha } = {z_{0.01}} = 2.33,\)and \(z = - 2.14\).

\(z < - {z_\alpha }\),so the null hypothesis is not rejected.

The \(0.01\) significance level and the customer should continue with the purchase.

Hence,

For significance level of \(0.05\) reject the null hypothesis.

For significance level of \(0.01\) do not reject the null hypothesis.

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Most popular questions from this chapter

The accompanying data on cube compressive strength (MPa) of concrete specimens appeared in the article 鈥淓xperimental Study of Recycled Rubber-Filled High-Strength Concrete鈥 (Magazine of Concrete Res., 2009: 549鈥556):

\(\begin{array}{l}112.3 97.0 92.7 86.0 102.0\\99.2 95.8 103.5 89.0 86.7\end{array}\)

a. Is it plausible that the compressive strength for this type of concrete is normally distributed?

b. Suppose the concrete will be used for a particular application unless there is strong evidence that true average strength is less than \(100MPa\). Should the concrete be used? Carry out a test of appropriate hypotheses.

A mixture of pulverized fuel ash and Portland cement to be used for grouting should have a compressive strength of more than 1300 KN/m2 . The mixture will not be used unless experimental evidence indicates conclusively that the strength specification has been met. Suppose compressive strength for specimens of this mixture is normally distributed with 蟽= 60. Let 碌 denote the true average compressive strength.

a.What are the appropriate null and alternative hypotheses?

b.Let \(\overline X \) denote the sample average compressive strength for n= 10 randomly selected specimens. Consider the test procedure with test statistic \(\overline X \) itself (not standardized). If \(\overline x = 1340\), should H0 be rejected using a significance level of .01? (Hint: What is the probability distribution of the test statistic when H0 is true?)

c.What is the probability distribution of the test statistic when 碌 = 1350? For a test with 伪 = .01, what is the probability that the mixture will be judged unsatisfactory when in fact 碌= 1350 (a type II error)?

For the following pairs of assertions, indicate which with our rules for setting up hypotheses and why (the subscripts 1 and 2 differentiate between quantities for two different populations or samples):

a. H0: 碌= 100, Ha: 碌 > 100

b.H0: 蟽= 20, Ha: \(\sigma \le 20\)

c.H0: p鈮 .25, Ha: p= .25

d.H0: 碌1 - 碌2 = 25, Ha: 碌1 - 碌2 > 100

e.H0: \(S_1^2 = S_2^2\) , Ha: \(S_1^2 \ne S_2^2\)

f.H0: 碌= 120, Ha: 碌= 150

g.H0: 蟽1,/蟽2 =1,Ha: 蟽1,/ 蟽2 鈮1

h.H0p1 鈥 p2 = -.1, Ha: p1 鈥 p2 < -.1

A plan for an executive travelers鈥 club has been developed by an airline on the premise that \(5\% \) of its current customers would qualify for membership. A random sample of \(500\) customers yielded \(40\) who would qualify.

a. Using this data, test at level \(.01\) the null hypothesis that the company鈥檚 premise is correct against the alternative that it is not correct.

b. What is the probability that when the test of part (a) is used, the company鈥檚 premise will be judged correct when in fact \(10\% \) of all current customers qualify?

A sample of n sludge specimens is selected and the pH of each one is determined. The one-sample t test will then be used to see if there is compelling evidence for concluding that true average pH is less than 7.0. What conclusion is appropriate in each of the following situations?

a.n= 6, t= -2.3, 伪= .05

b.n= 15, t= -3.1伪=.01

c.n= 12, t= -1.3, 伪= .05

d.n= 6, t = .7, 伪 = .05

e.n= 6, \(\overline x = 6.68,s/\sqrt n = .0820\)

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