Calculating probabilities

Here are two fair spinners. The total score is the sum of the two numbers the arrows point to.

Two fair spinners labelled (1-3) and (0-3) point to 2 and 1 respectively

Jot down, systematically, all the possible outcomes for the two spinners.

You will find it useful to use a table of results, as shown.

Triangular spinnerSquare spinnerTotal score
1 0 1
1 1 2
1 2 3
1 3 4
2 0 2
2 1 3
2 2 4
2 3 5
3 0 3
3 1 4
3 2 5
3 3 6

Use the table to answer these questions:

Question

How many different possible outcomes are there?

There are 12 possible outcomes.

All you have to do is count the number of entries in the table.

Question

How many outcomes give a total score of 2?

Only 2 outcomes give a total score of 2: a ' 1' on each spinner, or a ' 2' on the triangular spinner and ' 0' on the square one.

Question

What is the probability of getting a total score of 2?

The number of outcomes giving a total score of 2 over the number of outcomes possible = \frac{2}{{12}}or\frac{1}{6}

Question

How many outcomes give a total score of 4?

3 outcomes give a total score of 44.

Question

What is the probability of getting a total score of 44?

The number of outcomes giving a total score of 4 over the number of outcomes possible = \frac{3}{{12}}or\frac{1}{4}