<h2><u>Answer with explanation:</u></h2>
The confidence interval for population mean (when population standard deviation is unknown) is given by :-
, where n= sample size
= Sample mean
s= sample size
t* = Critical value.
Given : n= 25
Degree of freedom :
Significance level for 98% confidence interval :
Using t-distribution table ,
Two-tailed critical value for 98% confidence interval :
⇒ The critical value that should be used in constructing the confidence interval = 2.4922
Then, the 95% confidence interval would be :-
Hence, the 98% confidence interval for the mean repair cost for the dryers. =