In the following table, we see the monthly water consumption of a family during the first five months of 2004.

What is the average monthly consumption from January to May for this family, in $\mathrm{m}^{3}$?
(a) 11.3
(c) 12.7
(e) 317.5
(b) 11.7
(d) 63.5

| Months | Consumption $\left(\mathrm{m}^{3}\right)$ |
| :--- | :---: |
| January | 12.5 |
| February | 13.8 |
| March | 13.7 |
| April | 11.4 |
| May | 12.1 |
The correct option is (c).

Remember that the arithmetic mean of $n$ numbers is one $n$-th of the sum of these numbers. For example, the arithmetic mean of the numbers $3,6,8$ and 26 is

$$
\frac{3+6+8+26}{4}=\frac{43}{4}=10.75
$$

Similarly, the average monthly consumption is the sum of the monthly consumptions divided by the number of months. Therefore, the average monthly consumption is equal to

$$
\frac{12.5+13.8+13.7+11.4+12.1}{5}=12.7 \mathrm{~m}^{3}
$$