Answer: 29
Explanation:
It is important to know the definition.
The average of a set of number is defined as the sum of all these numbers divided by the total numbers that are in this set.
So, knowing this, we know that if we have a set of three numbers:"a", "b" and "c" , we can calculate the average of them with this procedure:
![average=(a+b+c)/(3)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/tbcb95a9zu3h5nnmechc56ebbbp4tp2m2a.png)
Therefore, we can calculate the average of the numbers 23, 33 and 31. This is: