Subtract. \[ \frac{2}{5}-\frac{1}{10}=\square \]

To subtract the fractions \(\frac{2}{5}\) and \(\frac{1}{10}\), we first need a common denominator. The least common multiple of 5 and 10 is 10. Now, convert \(\frac{2}{5}\) to an equivalent fraction with a denominator of 10: \[ \frac{2}{5} = \frac{2 \times 2}{5 \times 2} = \frac{4}{10} \] Now we can perform the subtraction: \[ \frac{4}{10} - \frac{1}{10} = \frac{4 - 1}{10} = \frac{3}{10} \] So, the answer is: \[ \frac{2}{5} - \frac{1}{10} = \frac{3}{10} \] And the box should be filled with \(\frac{3}{10}\).