9. 19 In Problem 9. 18 , how many degrees of freedom does the + test have ?" Solution : dif = ( 1 - 1 ) = 16 - 1 = 15 :` 9. 20 In Problems 9. 18 and 9. 19 , what are the critical values of I if the level of significance , is 0.05 and the alternative hypothesis , is Answer : Now since we have , it's going to be a two - tailed test , and as n = 16 we have 15 degrees of freedom ( Of = 17 - 1 ) . Looking over a t- distribution table the critical points would be