9. $A, B, C, D$ four people have some number of cards that are all different.
$A$ says: “I have 16 more cards than $C$.”
$B$ says: “$D$ has 6 more cards than $C$.”
$C$ says: “$A$ has 9 more cards than $D$.”
$D$ says: “If $A$ gives me 2 more cards, I will have 3 times as many cards as $C$.”
It is known that among these four people, the one with the fewest cards is the one who is wrong, and the others are right. How many cards does $D$ have?
【Answer】 10

【Solution】First, translate what each person said:
$A$ means: $A-C=16$;
$B$ means: $D-C=6$;
$C$ means: $A-D=9$;
$D$ means: $D+2=3 C$.
Since only one person is lying, and both $A$ and $C$ claim that $A$ is not the least, therefore, $A$ is telling the truth. From $B$ and $D$'s statements, we can infer that $D$'s number of cards is also not the least. Therefore, the liar can only be $B$ or $C$. If $C$ is telling the truth, then $\left\{\begin{array}{l}A-C=16 \\ A-D=9\end{array} \Rightarrow D-C=7\right.$, combined with $D+2=3 C$ leads to $C+7=3 C-2 \Rightarrow 9=2 C$, which has no integer solution, leading to a contradiction. Therefore, $B$ is telling the truth, and $C$ is lying. Using $B$'s conclusion, we have $\left\{\begin{array}{l}D-C=6 \\ D+2=3 C\end{array} \Rightarrow\left\{\begin{array}{l}C=4 \\ D=10\end{array}\right.\right.$ . Therefore, the answer is 10.