11. (6 points) There are six letter cards: $A$, $B$, $C$, $D$, $E$, $F$, arranged in a row, with the requirement that $A$ is placed at the left end and $F$ is placed at the right end. There are $\qquad$ different arrangements.
【Answer】Solution: $4 \times 3 \times 2=24$ (ways). Answer: There are 24 different ways to arrange them. Therefore, the answer is: 24.