High school math arrangement: 7 people stand in a row. If A can't stand in the middle, B can't stand at the left end and C can't stand at the right end, how many ways are there?

Indirect solution:

There are seven people standing in a row. * * * There is an arrangement of P77, with A standing in the middle, B at the left end and C at the right end. * * * There is P44, so the qualified arrangement is P77-P44.

(Note: Symbol P77 indicates the complete arrangement of 7)

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