2. Сократи дробь: 280/480; 17/51; 36/90; 13/65; 20/80.

1. \(\dfrac{280}{480}=\dfrac{280:40}{480:40}=\dfrac{7}{12}\).
2. \(\dfrac{17}{51}=\dfrac{17:17}{51:17}=\dfrac{1}{3}\).
3. \(\dfrac{36}{90}=\dfrac{36:18}{90:18}=\dfrac{2}{5}\).
4. \(\dfrac{13}{65}=\dfrac{13:13}{65:13}=\dfrac{1}{5}\).
5. \(\dfrac{20}{80}=\dfrac{20:20}{80:20}=\dfrac{1}{4}\).

Ответ: \(\dfrac{7}{12};\ \dfrac{1}{3};\ \dfrac{2}{5};\ \dfrac{1}{5};\ \dfrac{1}{4}\).