To divide fractions, you multiply by the reciprocal of the divisor. So, to find \( \frac{3}{10} \div \frac{1}{3} \), you can rewrite it as:
\[ \frac{3}{10} \times \frac{3}{1} \]
Now, multiply the numerators and the denominators:
\[ \frac{3 \times 3}{10 \times 1} = \frac{9}{10} \]
So, \( \frac{3}{10} \div \frac{1}{3} = \frac{9}{10} \).
The correct answer is \( \frac{9}{10} \).