Unit 2: Probability Lesson 2: Counting Our Way to Probabilities Classical Probability Formula: The challenging part of Classical probability is determining the sample size. Let's determine the sample size of rolling two six sided dice: Define Tree Diagram: Draw a tree diagram to help Susie determine the number of different outfits she can make. (You can draw on your own paper and insert an image below) Bottoms (Jeans, shorts, skirt, leggings), Tops (Red, Blue, Green, Yellow, or Pink), Head (Hat or no hat).