7. After an exam, if some of the high scores are removed in order, the class average will decrease; conversely, if some of the low scores are removed in order, the class average will increase. These two facts can be described mathematically as: if the finite sequence $a_{1}, a_{2}, \cdots, a_{n}$ satisfies $a_{1} \leqslant a_{2} \leqslant \cdots \leqslant a_{n}$, then $\qquad$ (the conclusion should be expressed in a mathematical formula).
7. $\frac{a_{1}+a_{2}+\cdots+a_{m}}{m} \leqslant \frac{a_{1}+a_{2}+\cdots+a_{n}}{n}(1 \leqslant m<n)$ and $\frac{a_{m+1}+a_{m+2}+\cdots+a_{n}}{n-m} \geqslant$ $\frac{a_{1}+a_{2}+\cdots+a_{n}}{n}(1 \leqslant m<n)$