Proving minimum number of chairs is $567$

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Jayant

Hints only please!

I am trying to figure this out somehow. A row can have as many girls, and a column can have as many boys.

Proof by contradiction seems like a good technique, but I am not sure how much it would help here.

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Let $r$ be the number of rows and $c$ be the number of columns. There are $14r$ boys and $10c$ girls along with $3$ empty seats. There are $rc$ seats in all. Thus, $14r+10c+3=rc$.

Subtracting $14r+3$ from both sides shows us that $10c=(c-14)r-3$ or $10c \equiv -3 \pmod r$.

Subtracting $10c+3$ from both sides shows us that $14r=(r-10)c-3$ or $14r \equiv -3 \pmod c$.

Not sure if this will lead you to the solution, but hopefully, these equations help!