How Do You Find the Probability of a Simple Event?

Drawing all of the marbles helps us count the different possibilities, which is a big part of finding probabilities!
We've circled the marbles that would give us a 'favorable outcome', which is that we either pick a green or a blue!
G stands for green marbles, and B stands for blue marbles
Combining the 5 green and 4 blue leads to 9 'favorable' outcomes
R stands for red marbles, and Y stands for yellow marbles
Adding all the marbles together tells us the total number of possible outcomes, and that represents the full sample space!
P(G or B) stands for the probability of picking a green or blue marble

1. We have a bag full of marbles, and we're picking only one marble
2. We need to know what the probability is that the one marble we pick will be green or blue
1. We have a bag full of marbles, and we're picking only one marble
2. Drawing a green or a blue marble is the 'event' we're looking for
1. A 'favorable outcome' is when what we want to happen happens
2. In this case, a favorable outcome is when we pull either a blue or a green marble!
1. Adding up the number of green and blue marbles helps us figure out how many ways we can get a favorable outcome!
1. All of the possible outcomes together define the 'sample space'
2. In this case, each marble represents a specific outcome
3. This means the total number of possible outcomes must be the total number of marbles!
1. If we want to know the total number of outcomes, then we can just count the number of marbles!
1. We can just divide the outcomes we want (favorable outcomes) by the total number of outcomes to find the probability
2. In other words, to find probability, just divide the number of green and blue marbles by the total number of marbles!
1. Remember, the favorable outcomes are what we want to happen
2. In this case, a favorable outcome is picking a green or blue marble!
3. The number of possible outcomes just means the total number of marbles that we could pick
4. We know that there are 9 ways to pick a green or a blue, and 29 total marbles we could pick
5. So dividing 9 by 29 will give us our answer:)

Suppose you draw one marble from a bag that has 5 green marbles, 9 red marbles, 4 blue marbles and 11 yellow marbles. What is the probability that you will draw either a green or blue marble?