\[\boxed{\mathbf{Страница\ 66.\ }\mathbf{Еуроки\ - \ ДЗ\ без\ мороки}}\]
\[\boxed{\mathbf{3.\ }}\]
\[\textbf{а)}\ 3 \cdot 4 = 12\ см^{2}.\]
\[\textbf{б)}\ (5 \cdot 4)\ :2 = 20\ :2 = 10\ см^{2}.\]
\[\textbf{в)}\ (5 \cdot 2)\ :2 = 10\ :2 = 5\ см^{2}.\]
\[\textbf{г)}\ 3 \cdot 5 - 5 \cdot 1\ :2 = 15 - 2,5 =\]
\[= 15,5\ см^{2}.\]
\[\textbf{д)}\ 3 \cdot 4 - 2 \cdot 2\ :2 - 2 \cdot 1\ :2 =\]
\[= 12 - 2 - 1 = 9\ см^{2}.\]
\[\boxed{\mathbf{4.\ }}\]