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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