4) 3/15 − 3/12

\(\frac{3}{15}=\frac{1}{5}\), \(\frac{3}{12}=\frac{1}{4}\). Тогда \(\frac{1}{5}-\frac{1}{4}=\frac{4}{20}-\frac{5}{20}=-\frac{1}{20}\).

Ответ: −1/20