You are going to construct a 99 interval on a population mea

You are going to construct a 99% interval on a population mean. The size of the sample taken was n = 20 and it was taken from a normal population. What is the correct value of t to use in the confidence interval formula?

CI = x ± t a/2 * (sd/ Sqrt(n))
Where,
x = Mean
sd = Standard Deviation
a = 1 - (Confidence Level/100)
ta/2 = t-table value
CI = Confidence Interval
Critical Value
The Value of |t | with n-1 = 19 d.f is 2.861