Find the critical value tc for the confidence level cequals 0.95 and sample size nequals 19.

The critical values are fixed values which can be obtained from the standard t crit tables. We can find the critical value tc when the degrees of freedom and confidence level are given. The degrees of freedom is simply:

Degrees of Freedom = Number of samples - 1

Degrees of Freedom = 19 - 1

Degrees of Freedom = 18

From the t critical tables, the tc corresponding to Degrees of Freedom equal to 18 and Confidence level equal to 95% is as follows:

tc = 2.101

Therefore this means that any t value beyond 2.101, we already reject the null hypothesis.