7. Put 48 chess pieces into 9 boxes, with at least 1 piece in each box, and the number of pieces in each box is different. The box with the most pieces can contain $\qquad$ pieces at most.

Put 48 chess pieces into 9 boxes, with at least 1 piece in each box, and the number of pieces in each box is different. The box with the most pieces can contain $\qquad$ pieces at most.
【Analysis】12 pieces
Key point: Maximum value problem;
When the total number of chess pieces is fixed, to make the number of chess pieces in the box with the most chess pieces as many as possible, the total number of chess pieces in the other 8 boxes should be as few as possible; and since the number of chess pieces in each box is different, the minimum total number of chess pieces in these 8 boxes is: $1+2+3+4+5+6+7+8=36$ pieces; therefore, the box with the most chess pieces can contain at most $48-36=12$ pieces.