A sample of size $n = 21$ is drawn from a normal population. Find the critical value needed to construct a $90 \%$ confidence interval.
A) 1.721
B) 1.645
C) 1.725
D) 1.325

Question

Quizplus · Accepted Answer

For a 90% confidence interval with a sample size of $n = 21$, we use the t-distribution because the population standard deviation is unknown. With $n - 1 = 20$ degrees of freedom, the closest critical value for a two-tailed test from t-distribution tables is approximately 1.725.

A Sample of Size n=21n = 21n=21 Is Drawn from a Normal Population

A Sample of Size $n = 21$ Is Drawn from a Normal Population