How to write down a simple probability as a fraction (math and statistics help).
Probability Basics Video
Probability is the likelihood of an event happening.
Using a fraction is the easiest way to express probability and this can be done by using the following formula:
(Number of successful outcomes)/(Total number of outcomes)
Probability can also be expressed as a decimal, and can take values between 0 and 1.
Let’s take a look at some examples:
Example 1
A bag contains 4 red balls, 7 blue balls and 5 green balls.
Write down the probability of picking a green ball from the bag.
The number of successful outcomes is 5 (as you are taking a green ball)
The total number of outcomes 4 + 7 + 5 = 16 (as this is the total amount of balls in the bag)
Therefore, the probability of picking a green ball is 5/16
Example 2
Another bag contains 6 black balls, 5 silver balls and 9 gold balls.
Write down the probability of picking a silver or gold ball from the bag.
This time the number of successful outcomes is 5 + 9 = 14 (as you are taking a silver or gold ball)
The total number of outcomes is 6 + 5 + 9 = 20.
Therefore, the probability of picking a silver or gold ball is 14/20 which can be simplified to 7/10.
Example 3
Work out the probability of rolling a number greater than 4 on a dice.
This time the number of successful outcomes is 2 (as there are 2 number larger than 4)
The total number of outcomes is 6 (as there are 6 numbers on a dice)
Therefore, the probability of rolling a number larger than 4 is 2/6 = 1/3
Example 4
Work out the probability of spinning a red on this spinner.
This time the number of successful outcomes is 2 (as there are 2 red sections on the spinner)
The total number of outcomes is 8 (as there are 8 sections in total)
Therefore, the probability of spinning a red is 2/8 = ¼.
