An experimenter wishes to investigate the effect of three variables, pressure, temperature, and the type of catalyst, on the yield in a refining process. If the experimenter intends to use three temperature settings and three pressure settings and two types of catalysts, how many experimental runs will have to be conducted if he wishes to run all possible combinations of pressure, temperature, and types of catalysts? I am a bit confused on all the different ways used to solve probability questions. This is what I have so far: 3 temp settings, 3 pressure settings, 2 types of catalysts And it is asking on how many possible different cominations of these 3 variables. There is 8 variables total. Whould this problem be an example of Multinomial Coefficients? so the way to solve is 8!/(3!*3!*2!) Is that correct? Thank you for your help.