Nine software engineers were interviewed to develop an estim

Nine software engineers were interviewed to develop an estimate for software lines of code. The mean estimate is 12480 lines of code with a standard deviation of 2000 lines of code. Develop a 90% confidence interval for the population mean. (Carry intermediate calculations to three decimal places.)

Solution

Note that              
Margin of Error E = t(alpha/2) * s / sqrt(n)              
Lower Bound = X - t(alpha/2) * s / sqrt(n)              
Upper Bound = X + t(alpha/2) * s / sqrt(n)              
              
where              
alpha/2 = (1 - confidence level)/2 =    0.05          
X = sample mean =    12480          
t(alpha/2) = critical t for the confidence interval =    1.859548038          
s = sample standard deviation =    2000          
n = sample size =    9          
df = n - 1 =    8          
Thus,              
Margin of Error E =    1239.698692          
Lower bound =    11240.30131          
Upper bound =    13719.69869          
              
Thus, the confidence interval is              
              
(   11240.30131   ,   13719.69869   ) [ANSWER]