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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

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

A regular type of laminate is currently being used by a manufacturer of circuit boards. A special laminate has been developed to reduce warpage. The regular laminate will be used on one sample of specimens and the special

laminate on another sample, and the amount of warpage will then be determined for each specimen. The manufacturer will then switch to the special laminate only if it can be demonstrated that the true average amount of warpage for that laminate is less than for the regular laminate. State the relevant hypotheses, and describe the type I and type II errors in the context of this situation.

Before agreeing to purchase a large order of polyethylene sheaths for a particular type of high-pressure oil filled submarine power cable, a company wants to see conclusive evidence that the true standard deviation of

sheath thickness is less than .05 mm. What hypotheses should be tested, and why? In this context, what are the type I and type II errors?

Let 碌 denote the true average radioactivity level (picocuries per liter). The value 5 pCi/L is considered the dividing line between safe and unsafe water. Would you recommend testing H0: 碌= 5 versus Ha: 碌> 5 or H0: 碌= 5 versus Ha: 碌 < 5? Explain your reasoning. (Hint: Think about the consequences of a type I and type II error for each possibility.)

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.

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