Calculate Probability

In this activity, we will look at a mix of probability questions.

 

Here is a recap of what we've learned on probability.

 

Writing Probability

A probability is given as a decimal, fraction or a percentage e.g 0.5, ½ or 50%

 

Displaying Probabilities

Remember that lists of possible outcomes, tables and tree diagrams are all useful ways to help you work out probabilities.

 

 

Calculating Probabilities

1) Probability of an event happening = Number of ways the event can happen ÷ Total number of possible outcomes

 

2) The probability of something not happening = 1 minus the probability of it happening.

 

3) You should also know when to add probabilities (or) and when to multiply them (and).

 

Example 1: Calculate the probability of throwing a 2 or a 5 on a six-sided die.

1/6 + 1/6 = 2/6   (OR rule, so we add)

 

Example 2: Calculate the probability of getting a heads on a coin and a 4 on a six-sided die.

1/2 × 1/6 = 1/12  (AND rule, so we multiply)

 

 

4) Relative frequency can be used to estimate an experimental probability. 

For example, if a coin is flipped 200 times, how many times can we expect it to land on tails?

The formula we use is : the probability x the number of times it was flipped

½ × 200 = 100

So, 100 is the number of times we might expect to throw tails.

 

Let's have a go at the questions now.

 

Remember that you can look back to this introduction at any time by clicking on the pink help button