what is/are the critical values?

Question

The data in the accompanying table represent the compressive​ strength, in thousands of pounds per square inch​ (psi), of 20 samples of concrete taken two and seven days after pouring. Complete parts​ (a) through​ (c) below.

at 0.01 level of significance

H0​: μD≥0 ​(where μD=μ1−μ2​)

H1​: μD<0

Tstat = -7.80

what is/are the critical values?

Answer 1

For tail alpha 0.01 and 19 degrees of freedom, the critical t value for a left-tailed test is -2.539.