t-student probability (p) look-up t 1.070 df 19 p (one tail) 0.149 P (two tails) 0.298 p (cumulative) 0.851 t-student look-up from p P (right tail) df 0.010 18 t (right tail) 2.552 p (left tail) df 0.010 18 t (left tail) -2.552 p (two tails) df 0.010 18 t (two tails) 2.878