An engineer has designed a valve that will regulate water pressure on an automobile engine. The valve was tested on 240240 engines and the mean pressure was 7.57.5 pounds/square inch (psi). Assume the population standard deviation is 1.01.0. The engineer designed the valve such that it would produce a mean pressure of 7.67.6 psi. It is believed that the valve does not perform to the specifications. A level of significance of 0.10.1 will be used. Find the P-value of the test statistic. Round your answer to four decimal places.

p-value = 0.1213  (to 4-decimal places)

Step-by-step explanation:

Given:

N = 240

mean  = 7.5

s = 1.0

Solution

With N=240 and using the central limit theorem, distribution can be approximated as normal.

Let

Null hypothesis H0, mu = 7.6

Alternate hypothesis, mu not equal to 7.6  (two-tail test)

for

Alpha = 0.1 (two sided)

Z = sqrt(N)(mean – mu)/s = sqrt(240)(7.5-7.6)/1.0 = -1.54919

p-value  

= P(|Z|>1.54919)  

= 2P(Z>1.54919)

= 2(1-P(Z<1.54919)

=2(1-0.9393)     (using normal distribution table)

=0.12134

Since alpha = 0.1 < p-value (0.1213), H0 that mean = 7.6 is not rejected.

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