Answer:
Step-by-step explanation:
The confidence interval for population mean is given by :-
Given : Sample mean : hours
Standard deviation hours
Sample size : n=90, which is a large sample(n<30), so we use z-test.
Significance level:
Critical value :
Then , the confidence interval for population mean will be :-
Hence, the 90% confidence interval for the mean life of all light bulbs of this type. is