A manufacturer claims that the mean lifetime of its light bulbs is 55 months. The standard deviation of these lifetimes is 6 months. Twenty-two bulbs are selected at random, and their mean lifetime is found to be 56 months. Assume that the population is normally distributed. Can we conclude, at the 0.05 level of significance, that the mean lifetime of light bulbs made by this manufacturer differs from 55 months?
Perform a two-tailed test. Then fill in the table below.
Carry your intermediate computations to at least three decimal places, and round your responses as specified in the table. (If necessary, consult a list of formulas.)
Please answer:
Ho=
H1=
Type of test?
The values of the test statistic?
The two critical values at the 0.05 level of significance?
Can we conclude that the mean lifetime of light bulbs made here differs from 55 months?