Question

The factory building manager at Delectable Delights, Jason Short, is concerned that the new contractor he hired is taking too long to replace defective lights in the factory workspace. He would like to perform a hypothesis test to determine if the replacement time for the lights under the new contractor is in fact longer than the replacement time under the previous contractor, which was 3.2 days on average. He selects a random sample of 12 service calls to replace defective lights and obtains the following times to replacement (in days). Use a significance level of

0.05. 6.2 7.1 5.4 5.5 7.5 2.6 4.3 2.9 3.7 0.7 5.6 1.7
1. Define μ in the context of the problem and state the appropriate hypotheses. (5 pts)
2. Regardless of your results in Part B, calculate the appropriate test statistic by hand. Write out all your steps.
3. What is your decision regarding the null hypothesis? (In other words, do you reject or fail to reject and why?)
4. Write a final concluding statement to Jason giving the results of the hypothesis test. (In other words, write the final summary statement.)

Answer 1

H0 : μ = 3.2

H1 : μ > 3.2

1.982

We fail to reject the Null ;

There is no significant evidence to conclude that the mean replacement time under the new contractor takes longer than the usual average time.

Explanation:

μ = average time taken by the previous contractor. ; μ = 3.2

H0 : μ = 3.2

H1 : μ > 3.2

Sample size, n = 12 ;

X = 6.2 7.1 5.4 5.5 7.5 2.6 4.3 2.9 3.7 0.7 5.6 1.7

xbar = Σx / n = 53.2 / 12 = 4.43

Standard deviation, s ; using a calculator :

s = 2.15

B.)

The test statistic :

(xbar - μ) ÷ (s / sqrt(n))

(4.43 - 3.2) ÷ (2.15 / sqrt(12))

1.23 ÷ 0.62065

= 1.982

C.)

Decision Region :

If Pvalue < α ; Reject the null

α = 0.05

Pvalue :

P(x < 1.982) = 0.9762

0.9762 > 0.05 ; Hence, we fail to reject the Null

There is no significant evidence to conclude that the mean replacement time under the new contractor takes longer than the usual average time.