Two fair spinners are divided into quarters as shown. One spinner shows the values 10, 30, 50 and 70.
The other spinner shows the values 1, 3, 5 and 7.
70 50
7
5
The two spinners are spun and the values shown are added to form a number.
For example, the diagram above would form the number 51.
Consider all the possible numbers that can be formed.
Calculate the probability of forming a number that is a multiple of 3.
You must show all your working in order to justify your answer.