\[\boxed{\mathbf{1.}}\]
\[34 \cdot 100 = 3400\]
\[1000 \cdot 750 = 750\ 000\]
\[300 \cdot 10\ 000 = 300\ 000\]
\[9000 \cdot 8 = 72\ 000\]
\[400 \cdot 80 = 32\ 000\]
\[50 \cdot 17\ 000 = 850\ 000\]
\[\boxed{\mathbf{2.}}\]
\[\textbf{а)}\ 12 \cdot 100 = 1200\]
\[1200\ :100 = 12\]
\[\textbf{б)}\ 40 \cdot 100 = 4000\]
\[4000\ :100 = 40\]
\[\textbf{в)}\ 90 \cdot 40 = 3600\]
\[3600\ :40 = 90\]
\[\textbf{г)}\ 200 \cdot 900 = 180\ 000\]
\[180\ 000\ :900 = 200\]
\[\boxed{\mathbf{3.}}\]
\[\textbf{а)}\ 358 + 52\ 071 + 79 + 970\ 537 =\]
\[= 1\ 023\ 045\]
\[\textbf{б)}\ 3\ 205\ 601 - (500\ 000 - 214) =\]
\[= 2\ 705\ 815\]
\[\boxed{\mathbf{4.}}\]
\[\textbf{а)}\ n\ :(n - 45) - страниц\ \]
\[больше\ в\ \ первой\ книге.\]
\[\textbf{б)}\ 10 \cdot (d\ :7)\ г - весят\ 10\ \ \]
\[пачек\ печенья.\]
\[\boxed{\mathbf{5.}}\]
\[\textbf{а)}\]
\[\textbf{б)}\]
\[с)\ \]