Probability Basics

Probability Basics

Theoretical Probability

The chance that some event will occur.


The theoretical probability of an event is a ratio that compares the number of favorable outcomes to the number of possible outcomes.

p(event) =  $\frac{number\ of\ favorable\ outcomes}{number\ of\ possible\ outcomes}$  

Probability an event will occur

Probability that an event will occur is a number from 0 to 1.

0 = 0% chance it will happen

1 = 100% chance it will happen

Finding Probability : Example 1

There are six equally likely outcomes on this spinner.
The possible outcomes are: red, yellow, green, orange, blue, and purple.
Find the probability of spinning and getting red.

P(red) =  $\frac{number\ of\ favoriable\ outcomes}{number\ of\ possible\ outcomes}$ 


= $\frac{1}{6}$  

Multiple Choice

On the spinner in the previous slide, what is the probability of spinning green?

• 1/6

• 2/6

• 1/2

You can have favorable outcomes that combines more than 1 outcome

Example 2

What is the probability of spinning yellow or red

P(yellow or red) = 2/6

Note the bottom number is still the total number of possible colors you can get.

Multiple Choice

What is the probability of spinning green, orange or purple?

P(green, orange, purple ) =

• 3/6

• 2/6

• 1/6

• 4/6

Multiple Choice

When rolling a regular 6-sided cube one time, what are the possible outcomes?

• 0, 1, 2, 3, 4, 5, 6

• 1, 6

• 1, 2, 3, 4, 5, 6

• 2, 4, 6

Multiple Choice

A bag has 3 red marbles, 2 blue and 4 yellow. What is the theoretical probability of randomly selecting a yellow marble?

• 4/10

• 4/9

• 1/9