15. (12 points) Chen Chen, a little kid, found that he has a total of 20 coins of 1 jiao and 5 jiao, and the total amount of money is 8 yuan. How many 1 jiao coins does he have?
【Answer】Solution: 8 yuan $=80$ jiao,
Assuming all are 5 jiao coins, then the 1 jiao ones are:
$$
\begin{aligned}
& (5 \times 20-80) \div(5-1) \\
= & 20 \div 4 \\
= & 5 \text { (pieces); }
\end{aligned}
$$

Answer: There are 5 pieces of 1 jiao coins.