9.6. In a certain company, there are 100 shareholders, and any 66 of them own no less than $50 \%$ of the company's shares. What is the largest percentage of all shares that one shareholder can own?
Solution. Let M be the shareholder owning the largest percentage of shares - x percent of shares. Divide the other 99 shareholders into three groups A, B, and

C, each with 33 shareholders. Let them own a, b, c percent of shares, respectively. Then

$$
2(100-x)=2(a+b+c)=(a+b)+(b+c)+(c+a) \geq 50+50+50
$$

That is, $x \leq 25$.

If each of the shareholders, except M, owns $\frac{75}{99}=\frac{25}{33} \%$ of the shares, then any 66 of them own exactly $50 \%$, and M owns exactly $25 \%$ of the shares.

Answer: $25 \%$ of the shares.