\[\boxed{\mathbf{Вариант\ 1.}}\]
\[\boxed{\mathbf{1.}}\]
\[1)\ 18 \cdot 20 + 18 \cdot 3 = 18 \cdot 23\]
\[18 \cdot (20 + 3) = 18 \cdot 23\]
\[2)\ 13 \cdot (40 + 6) > 13 \cdot 40 + 13\]
\[13 \cdot 40 + 13 \cdot 6 > 13 \cdot 40 + 13\]
\[\boxed{\mathbf{2.}}\]
\[1)\]
\[2)\ 50 \cdot (1256 - 978) = 13\ 900\]
\[\boxed{\mathbf{3.}}\]