If we have a number of equally likely and mutually exclusive outcomes for an experiment, then we can use the simple probability formula detailed below:

Exercise

Let’s complete exercise 3 from pages 294 to 296 of the core textbook:

The answers are below:

Expected Frequency

Based on this formula we have the concept of expected frequency.

If I role a dice 60 times, I would expect about 10 of the results to be “5” (though clearly I won’t always get exactly 10 “5”s. We say that the expected frequency of the outcome 5 is 10. We can calculate this as the probability multiplied by the number of trials, i.e. 1/6 x 60

Example

Exercise

Let’s complete exercise 4 from pages 296 and 297 of the core textbook:

The answers are below: