A sample set of weights in pounds are 1.01, .95, 1.03, 1.04, .97,

A sample set of weights in pounds are 1.01, .95, 1.03, 1.04, .97, .97, .99, 1.01, and 1.03. Assume the population of weights are normally distributed. Find a 99 percent confidence interval for the mean population weight.

I understand that I have to use the T table but I do not know how to obtain the sample standard deviation since I know the mean is 1 and the T statistic value is 3.355 and n=9.