3. In the chicken and rabbit cage, there are a total of 40 heads, the number of rabbit feet is 8 less than 10 times the number of chicken feet, so the number of rabbits is $\qquad$.
Analysis: Using the method of enumeration by approximation, since the number of rabbit feet is 9 times more than the number of chicken feet, and when the number of chickens and rabbits is the same, the number of rabbit feet is twice that of chicken feet, therefore, there are more rabbits than chickens. We can assume there are 35 rabbits, and adjust up or down to find the answer.
\begin{tabular}{|l|l|l|l|}
\hline Rabbits & 35 & 34 & 33 \\
\hline Rabbit feet & 140 & 136 & 132 \\
\hline Chicken feet & 10 & 12 & 14 \\
\hline Multiple of rabbit feet to chicken feet & $>10$ times & $>10$ times & \\
\hline
\end{tabular}

We can set up equations to solve the problem. Let the number of rabbits be $x$, then the number of chickens is $(40-x)$. According to the relationship of the number of feet, we can set up the equation:
$$
4 \mathrm{x}+8=10 \times 2 \times(40-\mathrm{x})
$$

Solving for $x$ gives $x=33$.