>> In the section following this one, we'll be studying probability. And in the study of probability counting possibilities in certain situations is very important. So in this section we're going to talk about counting principles. Consider this problem, suppose we flip a coin and then following that we roll a 6-sided die. And we'd like to know all of the possible outcomes in performing these 2 tasks, back to back. Well the safest thing to do in counting the possible outcomes in a situation like this is to list them all and simply count them. So now when we flip a coin, we know that there are 2 possibilities. We can either get a head or a tail. And when we roll this 6-sided die, we can get either a 1, a 2, a 3, a 4, a 5 or a 6. So one outcome is flipping a head and then rolling a 1. Another outcome is a head with a 2, head with a 3, head with 4, head with 5, head with a 6. And then we have to go through all of those possibilities if we flipped a tail on the flip of the coin so the tail could be associated with 1, T2, T3, T4, T5, T6. And then after listing all of the possibilities, we just count them: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. So there are 12 possible outcomes.