Simple Event

• Probability is the chance or likelihood that an event will happen. It is the ratio of the number of ways an event can occur to the number of possible outcomes. We'll use the following model to help calculate the probability of simple events.

Probability = # of ways a certain outcome can occur Total possible outcomes(sample space)

Example 1

Given a standard number cube, determine the probability for the following events.P(5)P(even number)P(7)

First identify the sample space. The sample space then becomes the denominator in the fraction.Sample Space is 6

• P(5) = There is 1 #5 on a die, so there’s 1 chance of rolling a 5. Our sample space is 6 because there are 6 numbers on that die.

• P(even number) = There are 3 even numbers (2,4,6). Our sample space is still 6.

• P(7) = 0This is impossible because a standard number cube (a die) has only 6 sides.

Example 2

There are 4 blue marbles, 5 red marbles, 1 green marble, and 2 black marbles in a bag. Suppose you select one marble at random. Find the probability that you will select…P(black)P(blue or black)P(not green)

The sample space is12

P(black) =

P(blue or black) =

P(not green) =