\[\boxed{\mathbf{Страница\ 54.\ }\mathbf{Еуроки\ - \ ДЗ\ без\ мороки}}\]
\[\boxed{\mathbf{6.\ }}\]
\[(1800 - 1000)\ :10 - 68 =\]
\[= 80 - 68 = 12\ \left( \frac{км}{ч} \right) -\]
\[увеличена\ скорость\ поезда.\]
\[Ответ:на\ 12\ \frac{км}{ч}.\]
\[\boxed{\mathbf{7.\ }}\]
\[\textbf{а)}\ 78 \cdot 35 + 22 \cdot 35 =\]
\[= (78 + 22) \cdot 35 =\]
\[= 100 \cdot 35 = 3500\]
\[\textbf{б)}\ 8 \cdot 7 + 8 \cdot 4 = (7 + 4) \cdot 8 =\]
\[= 11 \cdot 8 = 88\]
\[\textbf{в)}\ 42 \cdot 42 - 32 \cdot 42 + 10 \cdot 42 =\]
\[= 42 \cdot (42 - 32 + 10) =\]
\[= 42 \cdot 20 = 840\]
\[\textbf{г)}\ 19 \cdot 17 + 11 \cdot 17 =\]
\[= 17 \cdot (19 + 11) =\]
\[= 17 \cdot 30 = 510\]
\[\textbf{д)}\ 7 \cdot 379 - 6 \cdot 379 =\]
\[= 379 \cdot (7 - 6) =\]
\[= 379 \cdot 1 = 379\]
\[\textbf{е)}\ 19 \cdot 65 + 12 \cdot 65 - 31 \cdot 65 =\]
\[= 65 \cdot (19 + 12 - 31) =\]
\[= 65 \cdot 0 = 0\]
\[\textbf{ж)}\ 16 \cdot 83 + 19 \cdot 83 - 32 \cdot 83 =\]
\[= 83 \cdot (16 + 19 - 32) =\]
\[= 83 \cdot 3 = 249\]
\[\textbf{з)}\ 927 \cdot 18 - 927 \cdot 17 =\]
\[= 927 \cdot (18 - 17) =\]
\[= 927 \cdot 1 = 927\]
\[\textbf{и)}\ 36 \cdot 52 + 54 \cdot 52 =\]
\[= 52 \cdot (36 + 54) =\]
\[= 52 \cdot 90 = 4680\]