Chance
Probability or chance is how likely something is to happen:
- If something has a low probability, it is unlikely to happen.
- If something has a high probability, it is likely to happen.
How to express probability
There are two main methods of expressing probability:
- Probabilities are most commonly shown as fractions:
- The probability of getting 'tails' when you toss a coin is a 1 in 2 chance, or 1/2
- The probability of getting a 3 when you roll a dice is a 1 in 6 chance, or1/6
- The probability of getting 'tails' when you toss a coin is a 1 in 2 chance, or 1/2
- Probabilities can also be shown as decimals or percentages:
- A probability of 1/2 can also be shown as 0.5 or 50%
- A probability of 3/4 can also be shown as 0.75 or 75%
- A probability of 1/2 can also be shown as 0.5 or 50%
Probability scales
Probabilities can be shown on a scale between 0 (impossible) and 1 (certain).
For example, imagine a shopping bag contains three bananas and nothing else:
- The probability of reaching into the bag and pulling out a banana is 1 (certain), as there is nothing else in the bag.
- The probability of reaching into the bag and pulling out an apple is 0 (impossible), as there are no apples in the bag.
Working out probability
Work out the probability of throwing an even number on a dice.
- Count up the total number of possible results.
When throwing a dice, for example, there are 6 possible numbers the dice can land on (1, 2 ,3 ,4, 5, 6). - Then count up the number of results you are interested in.
In this example, you are only interested in throwing a 2, 4 or 6 (all the even numbers on a dice). So you are interested in 3 numbers. - The probability of getting an even number on a dice is 3 chances out of 6 chances which you write as 3/6.
3/6 is the same as 1/2 which can also be expressed as 'half', 0.5 or 50%.