\[\boxed{\ \mathbf{685\ (685)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 28 \cdot \frac{1}{2} = 28\ :2 = 14\]
\[2)\ 28 \cdot \frac{3}{7} = 28\ :7 \cdot 3 = 4 \cdot 3 = 12\]
\[3)\ 28 \cdot \frac{9}{14} = 28\ :14 \cdot 9 =\]
\[= 2 \cdot 9 = 18\]
\[4)\ 28 \cdot \frac{19}{28} = 28\ :28 \cdot 19 = 19\]