Question

An engineer has designed a valve that will regulate water pressure on an automobile engine. The engineer designed the valve such that it would produce a mean pressure of 6.9 pounds/square inch. The valve was tested on 13 engines and the mean pressure was 6.7 pounds/square inch with a variance of 0.49. Is there evidence at the 0.1 level that the valve performs below the specifications? Assume the population distribution is approximately normal.

Step 2 of 5:

Find the value of the test statistic. Round your answer to three decimal places.

Answer 1

Solution :

This is the two tailed test,  

The null and alternative hypothesis is ,

H0 :   = 6.9

Ha : < 6.9

Test statistic = t =

= ( - ) / s / n

= (6.7 - 6.9 ) / 0.7 / 13

Test statistic = t = -1.030