11. (5 points) As shown in the figure, two iron rods are vertically placed in a wooden bucket with a flat bottom. After adding water to the bucket, the length of one iron rod above the water is $\frac{1}{3}$ of its total length, and the length of the other iron rod above the water is $\frac{1}{5}$ of its total length. Given that the sum of the lengths of the two iron rods is 33 cm, the difference in length between the two iron rods is $\qquad$ cm.
【Solution】Solution: Let the underwater length of the two iron rods be $x$ cm. According to the problem, we can get the equation:
$$
\begin{array}{l} 
x \div \frac{2}{3}+x \div \frac{4}{5}=33 \\
\frac{3}{2} x+\frac{5}{4} x=33 \\
\frac{11}{4} x=33 \\
x=12
\end{array}
$$

Then the difference in length of the two iron rods is:
$$
\begin{array}{l}
12 \div \frac{2}{3}-12 \div \frac{4}{5} \\
=18-15, \\
=3 \text { (cm); }
\end{array}
$$

Answer: The difference in length of the two iron rods is 3 cm.
Therefore, the answer is: 3.