Probabilities not in Table C. There are times you may need to determine a probability for a t-random variable that does not appear in Table C. For example, you may need to determine the probability a t-random variable with 8 degrees of freedom is greater than 2.65.

Even though this value is not in Table C, you can still get a good idea of its probability by bracketing it between two landmarks in the table. In this case, 2.65 is bracketed between t8,0.975

(2.306) and t8,0.99

(2.896). Therefore, it has a cumulative probability that is a little bigger than 0.975 and a little smaller than 0.99. What is the probability of t8 > 2.65? In other words, what is the probability of observing a t random variable with 8 df that is greater than 2.65?