453. Find the sample mean for the given distribution of sample size $n=10$ :

| $x_{i}$ | 1250 | 1270 | 1280 |
| :--- | :---: | :---: | :---: |
| $n_{i}$ | 2 | 5 | 3 |
Solution. The initial variants are large numbers, so we will switch to conditional variants $u_{i}=x_{i}-1270$. As a result, we will get the distribution of conditional variants:

$$
\begin{array}{rrrr}
u_{i} & -20 & 0 & 10 \\
n_{i} & 2 & 5 & 3
\end{array}
$$

We will find the required sample mean:

$$
\bar{x}_{\mathrm{B}}=C+\frac{\sum n_{i} u_{i}}{n}=1270+\frac{2 \cdot(-20)+5 \cdot 0+3 \cdot 10}{10}=1270-1=1269
$$