Concept

Probability tells you the likelihood of an event happening. The higher the probability, the more likely it is to happen. 

Probability is a number or fraction between 0 and 1. A probability of 1 means something will always happen, and a probability of 0 means something will never happen.

Rule

To write the probability as a fraction:

P (E) = (Number of desired outcomes)(Total number of possible outcomes)

Reduce the fraction by dividing the numerator and denominator by their greatest common factor.

To convert the probability from a fraction into a decimal or percent:
Step 1: Find a number to multiply by the denominator to make it 100.
Step 2: Multiply both numerator and denominator by that number, making an equivalent fraction.
Step 3: Write the decimal and/or percent using the correct place value position.

Example

A student has a deck of 50 cards numbered 1-50. What is the probability of the student choosing a multiple of 6 from the deck?

Write your answer as a decimal.

Solution

To write the probability as a fraction:

P (E) = (Number of desired outcomes)(Total number of possible outcomes)

Step 1: Find the total number of possible outcomes.
Since there are 50 cards in the deck, there are 50 possible outcomes.

Step 2: Find the number of desired outcomes.
There are 8 cards that are multiples of 6

Step 3: P(multiples of 6) = 850

Step 4: Reduce the fraction.

8 ÷ 250 ÷ 2 = 425

Convert the fraction to a decimal.

Step 1: Find a number to multiply by the denominator to make it 100.

25 × 4 = 100

Step 2: Make an equivalent fraction

4 × 425 × 4 = 16100

Step 3: Write the decimal using the correct place value position.

16100 = 0.16

Pre-requisite Skills

Convert Fractions/Decimals to Percents (6.8.2)

Equivalent Fractions (5.10.5)

Simplifying fractions (5.10.6)