Suppose You Have a Random Sample of 21 Credit Scores $\left( \frac { 70 } { \sqrt { 21 } } \right)$

Suppose you have a random sample of 21 credit scores from a population of mortgage applicants with a sample mean of 620 and sample standard deviation of 70, and would like to calculate the 99 percent confidence interval of the population mean credit score. Which of the following would be the correct construction?

A) 620 ± 2.58 $\left( \frac { 70 } { \sqrt { 21 } } \right)$
B) 620 ± 4 $\left( \frac { 70 } { \sqrt { 21 } } \right)$ , because 4 is the t-distribution critical value.
C) 620 ± 4 (70) , because 4 is the t-distribution critical value.
D) None of these choices are correct.