3. (6 points) 2 fen and 5 fen coins total 15, with a total value of 51 fen. The 2 fen coins are $\qquad$ more than the 5 fen coins.
【Answer】Solution: Assume all are 5-cent coins,
$$
\begin{array}{l}
2 \text { cents: }(5 \times 15-51) \div(5-2), \\
=24 \div 3, \\
=8 \text { (coins); } \\
5 \text { cents: } 15-8=7 \text { (coins); } \\
8-7=1 \text { (coin); }
\end{array}
$$

Answer: The 2-cent coins are 1 more than the 5-cent coins. Therefore, the answer is: 1.