To solve \( \frac{3}{10} \div \frac{1}{3} \), we can multiply by the reciprocal of the second fraction:
\[ \frac{3}{10} \div \frac{1}{3} = \frac{3}{10} \times \frac{3}{1} = \frac{3 \times 3}{10 \times 1} = \frac{9}{10} \]
So the answer is \( \frac{9}{10} \).