Probability

Probability tells us how likely is that something will happen. It can be written as a decimal, fraction or percentage. We can even describe probabilities using words.

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The common terms we use are:

ย Probability scales are also very useful to describe probabilities. This scale ranges from 0 to 1. 0 refers to impossibility and 1 refers to when something is certain.

This is an example of a probability scale. As you can see on the scale, it is certain that Christmas will be on 25th December this year.


Letโ€™s have a look at this question:

Finding probabilities

There are 6 numbers on a die. What is the probability of rolling an odd number?

Firstly, there are 3 odd numbers in total on a die โ€“ 1, 3 and 5.

This means that there are 3 possibilities. So, the probability of rolling an odd number: \frac { 3 }{ 6 } =50% chance.


Finding the sum of probabilities

Note: the sum of probabilities should equal to 1.

The probability of tossing a head of a coin is \frac { 1 }{ 2 } and the probability of tossing a tail of a coin is \frac { 1 }{ 2 }.  \frac { 1 }{ 2 } +\frac { 1 }{ 2 } =1.

If you go to school, the probability of you being early is 3/8, what is the probability that you will be late?

1-\frac { 3 }{ 8 } =\frac { 5 }{ 8 }

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