The $\frac{80}{20}$ principle means that:

when $80\%$ of a firm's consumers are satisfied, profits will increase by $20\%.$

none of these.

$80-$year$-$old consumers have significantly more resources than $20-$year$-$old consumers and thus constitute a more attractive target market.

roughly $80\%$ of a firm's profit comes from $20\%$ of its sales.

approximately $20\%$ of a firm's consumers generate $80\%$ of sales.