Question

A random sample of 20 items is selected from a population. to determine the appropriate critical t-value what number of degrees of freedom should be used?

Answer 1

The t-distribution has n - 1 degrees of freedom, where n is the sample size.
In this case n = 20. So the required number of degrees of freedom is:            
 20 - 1 = 19.
The answer is: 19 degrees of freedom.