# Probability Problems

In this lesson we will learn how to solve simple probability problems with a number cube. Double-click the play button to watch the following video.

## Definition

The probability of an event measures the likelihood that the event will occur.

## Formula

When trying to find the probability of an event, use this formula:

### P(event) = number of favorable outcomes / total number of outcomes

When solving problems about a number cube (or a die), you should know that the total number of outcomes is 6, because a cube has six faces. Therefore, the denominator is six. To find the numerator, count the number of favorable outcomes. Let's try some examples.

## Example 1

A die is rolled once. What is the probability of getting an odd number?

## Solution

The following outcomes are favorable: getting number 1, getting number 3, or getting number 5.

There are 3 favorable outcomes (the above outcomes). Therefore the numerator is 3.

The denominator is 6 because there are 6 unique numbers on a die.

P(odd number) = 3/6 = 1/2 = 0.50 = 50%

## Example 2

A die is rolled once. What is the probability of getting a prime number less than four?

## Solution

2 and 3 are the only prime numbers less than four. Since there are two favorable outcomes, the numerator is two.

The denominator is 6 because there are 6 unique numbers on a die.

P(prime number less than 4) = 2/6 = 1/3 = 0.333... = 33%

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