Over the week we started chapter 16. It was all about different types of probability. The two most popular types (that we used anyway) had to do with a standard deck of cards or with rolling two dice.

When working with probability, your answer will almost always be a fraction. There are two exceptions to this. If the event is absolutely impossible, the answer is zero. If the event is going to happen no matter what, the answer is one. Your answer can also be expressed as a percent.

The formula for probability is as follows:
P(event eight)= number of favorable outcomes/total number of outcomes

Here is another formula:
P(A or B)=P(A)+P(B)-P(A and B)

If something is mutually exclusive, it is impossible for both events to happen at the same time. The formula for something that is mutually exclusive is as follows:
P(A or B)=P(A)+P(B)

EXAMPLE:
A standard deck of cards has suits: spades, hearts, clubs, and diamonds. Each suit has thirteen cards. Of those cards, nine have numbers, three have faces, and one is an ace. What is the probability that you pick a card that is
A) An even number
P(even number)=5/52

B) A black card
P(black card)=26/52 = ½

C) A red spade
P(red spade) 0/52=0

--Sarah