Complete parts (a) through (c) below.

(a) Determine the critical value(s) for a right-tailed test of a population mean at the alpha = 0.10 level of significance with 20 degrees of freedom.
(b) Determine the critical value(s) for a left-tailed test of a population mean at the alpha = 0.05 level of significance based on a sample size of n=10.
(c) Determine the critical value(s) for a two-tailed test of a population mean at the alpha=0.01 level of significance based on a sample size of n=11.

a)

For this case the value of , since is a right tailed test we need a critical value on the t distribution with 19 degrees of freedom that accumulates 0.1 of the area on the right and we got:

b)

For this case the value of , since is a left tailed test we need a critical value on the t distribution with 9 degrees of freedom that accumulates 0.05 of the area on the right and we got:

c)

For this case the value of and , since is a two tailed tailed test we need a critical value on the t distribution with 10 degrees of freedom that accumulates 0.005 of the area on both tails and we got:

Step-by-step explanation:

Previous concepts

The t distribution (Student’s t-distribution) is a "probability distribution that is used to estimate population parameters when the sample size is small (n<30) or when the population variance is unknown".

The shape of the t distribution is determined by its degrees of freedom and when the degrees of freedom increase the t distirbution becomes a normal distribution approximately.  

The degrees of freedom represent "the number of independent observations in a set of data. For example if we estimate a mean score from a single sample, the number of independent observations would be equal to the sample size minus one."

Solution to the problem

Part a

We can calculate the degrees of freedom first:

For this case the value of , since is a right tailed test we need a critical value on the t distribution with 19 degrees of freedom that accumulates 0.1 of the area on the right and we got:

Part b

We can calculate the degrees of freedom first:

For this case the value of , since is a left tailed test we need a critical value on the t distribution with 9 degrees of freedom that accumulates 0.05 of the area on the right and we got:

Part c

We can calculate the degrees of freedom first:

For this case the value of and , since is a two tailed tailed test we need a critical value on the t distribution with 10 degrees of freedom that accumulates 0.005 of the area on both tails and we got: