To divide \( \frac{3}{10} \) by \( 4 \), you can rewrite the division of a fraction by a whole number as multiplying by the reciprocal of the whole number:
\[ \frac{3}{10} \div 4 = \frac{3}{10} \times \frac{1}{4} \]
Now, multiply the fractions:
\[ \frac{3 \times 1}{10 \times 4} = \frac{3}{40} \]
So, \( \frac{3}{10} \div 4 = \frac{3}{40} \).