A simple random sample of textbooks in a local college books

A simple random sample of textbooks in a local college bookstore yielded a mean textbook cost of $74.80 with a standard deviation of $19.79. Find an 85% confidence interval for the true mean cost of a college textbook.

Solution

Size of the sample is n\'t provided, calculated by assuming the sample size as one.

CI = x ± Z a/2 * (sd/ Sqrt(n))
Where,
x = Mean
sd = Standard Deviation
a = 1 - (Confidence Level/100)
Za/2 = Z-table value
CI = Confidence Interval
Mean(x)=74.8
Standard deviation( sd )=19.79
Sample Size(n)=1
Confidence Interval = [ 74.8 ± Z a/2 ( 19.79/ Sqrt ( 1) ) ]
= [ 74.8 - 1.44 * (19.79) , 74.8 + 1.44 * (19.79) ]
= [ 46.3,103.3 ]