7. Let the number filled in the $i$-th row and $j$-th column of a $5 \times 5$ grid be $a_{i j}\left(a_{i j} \in\{0,1\}\right), a_{i j}=a_{j i}(1 \leqslant i, j \leqslant 5)$. Then the total number of ways to fill the grid with exactly five 1s is $\qquad$ (answer with a specific number).
ニ,7.326.
The total number of valid filling methods is
$$
\mathrm{C}_{5}^{1} \mathrm{C}_{10}^{2}+\mathrm{C}_{5}^{3} \mathrm{C}_{10}^{1}+\mathrm{C}_{5}^{5}=326
$$