Решебник по математике 5 класс Мерзляк ФГОС Задание 744

\[\boxed{\mathbf{744\ (744)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ \frac{5}{19} + \frac{6}{19} = \frac{5 + 6}{19} = \frac{11}{19}\]

\[2)\ \frac{7}{13} - \frac{4}{13} = \frac{7 - 4}{13} = \frac{3}{13}\]

\[3)\ \frac{19}{25} + \frac{4}{25} - \frac{22}{25} =\]

\[= \frac{19 + 4 - 22}{25} = \frac{1}{25}\]

\[4)\ \frac{34}{39} - \frac{15}{39} - \frac{8}{39} =\]

\[= \frac{34 - 15 - 8}{39} = \frac{11}{39}\]

\[\boxed{\mathbf{744}\mathbf{\ (572)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]

\[P_{пр} = 4\ м\ 8\ дм = 48\ дм;\ \ a = 5b\]

\[P_{пр} = 2 \cdot (a + b) = 48\ дм.\]

\[5b + b = 48\ :2\]

\[6b = 24\]

\[b = 4\ дм.\]

\[a = 5b = 5 \cdot 4 = 20\ дм.\]

\[S = a \cdot b = 20 \cdot 4 = 80\ дм^{2}.\]

\[Ответ:80\ дм^{2}.\]