Question

An engineer has designed a valve that will regulate water pressure on an automobile engine. The valve was tested on 130 engines and the mean pressure was 4.5 pounds/square inch (psi). Assume the population standard deviation is 0.9. The engineer designed the valve such that it would produce a mean pressure of 4.7 psi. It is believed that the valve does not perform to the specifications. A level of significance of 0.02 will be used. Make the decision to reject or fail to reject the null hypothesis.

Answer 1

Solution :

= 4.7

=4.5

=0.9

n = 130

This is the two tailed test .

The null and alternative hypothesis is ,

H0 :    = 4.7

Ha :     4.7

Test statistic = z

= ( - ) / / n

= (4.5 -4.7 ) / 0.9 / 130

= -2.53

Test statistic = z = -2.53  

P-value = 2 * 0.0057 =0.0114

= 0.02

P-value <

0.0114 < 0.02

Reject the null hypothesis .

There is sufficient evidence to suggest that