G5.1 If $a$ is a positive multiple of 5 , which gives remainder 1 when divided by 3 , find the smallest possible value of $a$. (Reference: 1998 FSG.1)
$$
\begin{array}{l}
a=5 k=3 m+1 \\
5 \times 2=3 \times 3+1
\end{array}
$$

The smallest possible $a=10$.