Решебник по математике 5 класс Ерина. Никольский рабочая тетрадь Часть 1, 2 Часть 1 | Страница 23

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\[\boxed{\mathbf{8.}}\]

\[1)\ (1800 - 1000)\ :10 =\]

\[= 800\ :10 = 80\ \left( \frac{км}{ч} \right) -\]

\[должна\ быть\ скорость\ поезда.\]

\[2)\ 80 - 68 = 12\ \left( \frac{км}{ч} \right) - на\ \]

\[столько\ \ была\ увеличена\ \]

\[скорость\ поезда.\]

\[Ответ:на\ 12\ \frac{км}{ч}.\]

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\[\textbf{а)}\ 78 \cdot 35 + 22 \cdot 35 =\]

\[= 35 \cdot (78 + 22) =\]

\[= 35 \cdot 100 = 3500\]

\[\textbf{б)}\ 19 \cdot 17 + 11 \cdot 17 =\]

\[= 17 \cdot (19 + 11) =\]

\[= 17 \cdot 30 = 510\]

\[\textbf{в)}\ 42 \cdot 42 - 32 \cdot 42 + 10 \cdot 42 =\]

\[= 42 \cdot (42 - 32 + 10) =\]

\[= 42 \cdot 20 = 840\]

\[\textbf{г)}\ 7 \cdot 379 - 6 \cdot 379 =\]

\[= 379 \cdot (7 - 6) = 379\]

\[\textbf{д)}\ 19 \cdot 65 + 12 \cdot 65 - 31 \cdot 65 =\]

\[= 65 \cdot (19 + 12 - 31) =\]

\[= 65 \cdot 0 = 0\]

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\[\textbf{а)}\ 13x + 16x = (13 + 16)x =\]

\[= 29x\]

\[\textbf{б)}\ 48p - 27p = (48 - 27)p =\]

\[= 21p\]

\[\textbf{в)}\ 13a + 5a - a =\]

\[= (13 + 5 - 1)a = 17a\ \]

\[\boxed{\mathbf{11.}}\]

\[\textbf{а)}\ 8x + 8x = 320\]

\[16x = 320\]

\[x = 320\ :16\]

\[x = 20.\]

\[\textbf{б)}\ 10a - a = 810\]

\[9a = 810\]

\[a = 810\ :9\]

\[a = 90.\]

\[\textbf{в)}\ 5t + 4t + t = 720\]

\[10t = 720\]

\[t = 720\ :10\]

\[t = 72.\]

\[\textbf{г)}\ 14b + 6b = 400\]

\[20b = 400\]

\[b = 400\ :20\]

\[b = 20.\ \]

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\[\textbf{а)}\ x = 37:\]

\[7x + 9x + 4x = 20x =\]

\[= 20 \cdot 37 = 740.\]

\[\textbf{б)}\ x = 7:\]

\[24x + 9x - 22x + 23 =\]

\[= 11x + 23 = \ 11 \cdot 7 + 23 =\]

\[= 77 + 23 = 100.\]