A manufacturer claims that the mean lifetime, u, of its light bulbs is 48 months. The standard deviation of these lifetimes is 5 months. Eighty bulbs are selected at random, and their mean lifetime is found to be 49 months. Can we conclude, at the 0.05 level of significance, that the mean lifetime of light bulbs made by this manufacturer differs from 48 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.)
The null hypothesis?
The alternative hypothesis?
The type of test statistic: Z
The value of the statistic test?
The p value?
Can we conclude that the mean lifetime differs from 48 months?