Dullco Manufacturing claims that its alkaline batteries last at least 40 hours on average in a certain type of portable CD player. But tests on a random sample of 18 batteries from a day's large production run showed a mean battery life of 37.8 hours with a standard deviation of 5.4 hours. To test DullCo's hypothesis, the test statistic is:

Select one:

a. - 2.101

b. - 1.980

c. - 1.960

d. - 1.728

lyrics d - 1.782

Step-by-step explanation:

Assume Normal Distribution

we have μ₀ = 40 (from Dullco claims)

And from sample μ = 37.8 and standard deviation of 5.4

random sample n = 18

We have to use t-student for testing the hypothesis

and we have a one tail test (left) since Dullco claims : " at least" meaning (always bigger or at least) not different.

Then

t (s) = (μ - μ₀) / (σ/√n) ⇒ t (s) = [ (37.8 - 40) * √18 ]/5.4

t (s) = - 1.7284