\[\boxed{\mathbf{1.}}\]
\[34 \cdot (10 \cdot 2) = 34 \cdot 2 \cdot 10 =\]
\[= 68 \cdot 10 = 680\]
\[19 \cdot (10 \cdot 5) = 19 \cdot 5 \cdot 10 =\]
\[= 95 \cdot 10 = 950\]
\[27 \cdot (3 \cdot 10) = 27 \cdot 3 \cdot 10 =\]
\[= 81 \cdot 10 = 810\]
\[12 \cdot (7 \cdot 10) = 12 \cdot 7 \cdot 10 =\]
\[= 84 \cdot 10 = 840\]
\[23 \cdot (10 \cdot 3) = 23 \cdot 3 \cdot 10 =\]
\[= 69 \cdot 10 = 690\]
\[45 \cdot (2 \cdot 10) = 45 \cdot 2 \cdot 10 =\]
\[= 90 \cdot 10 = 900\]
\[\boxed{\mathbf{2.}}\]
\[\boxed{\mathbf{3.}}\]
\[(100\ :5 + 5) \cdot 40 = 1000\]
\[100\ :(5 + 5) \cdot 40 = 400\]
\[\boxed{\mathbf{4.}}\]
\[240\ :10 - 72\ :6 = 24 - 12 =\]
\[= 12\ (рублей) - килограмм\ \]
\[свеклы\ дороже\ килограмма\ \]
\[капусты.\]
\[Ответ:на\ 12\ рублей.\]