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How to write down a simple probability as a fraction (math and statistics help).

Updated on April 16, 2013

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.

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    LLAMA!!! 5 years ago

    Very helpful, this helped me remember it for the exam ^_^!!