7. \(\frac{2}{5}-\frac{10}{15}\)

Сократим дробь: \(\frac{10}{15}=\frac{2}{3}\).

\(\frac{2}{5}-\frac{2}{3}=\frac{6}{15}-\frac{10}{15}=-\frac{4}{15}\).

Ответ: \(-\frac{4}{15}\)