Find the critical value t a/2 needed to construct a confidence interval of the given level with the given sample size. level 95%, sample size 11

Α = 1- (95/100) = 1-0.95 = 0.05

p = 1- α/2 = 1- 0.05/2 = 1-0.025 = 0.975

Degrees of freedom, df = Sample size -1 = 11-1 = 10

From t-tables, with cumulative probability pf 0.975 and df of 10,
Critical value = 2.228