ProbabilityBasic probabilities

The link between simple probability and expected frequency is explored. The idea of risk is investigated and its impact on life.

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Basic probabilities

Words like 'certain', 'likely' and so on, may not mean the same to everyone.

We need to be more precise about how likely something (an outcome) is to happen.

The probability of an outcome can have any value between \(0\) (impossible) and \(1\) (certain). It can be written as a fraction, decimal or percentage.

We can calculate a value for the probability using the formula:

\(Probability\,of\,an\,outcome = \frac{{number\,of\,ways\,the\,outcome\,can\,happen}}{{total\,number\,of\,possible\,outcomes}}\)

When you throw a fair die there are six possible outcomes: \(1,\,2,\,3,\,4,\,5\,or\,6\).

There are three ways of getting an odd number (\(1,\,3\,or\,5\)).

So the probability of getting an odd number = the number of ways of getting an odd number ÷ total number of possible outcomes.

\(= \frac{3}{6} = \frac{1}{2}\)

Which can also be written as or \(0.5\), or \(50\%\).

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