\[\boxed{\ \mathbf{929\ (929)}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ a = 4;\ \ b = 6,8:\]
\[0,5a \cdot 20b = 10ab =\]
\[= 10 \cdot 4 \cdot 6,8 = 40 \cdot 6,8 = 272.\]
\[2)\ x = 1,2;\ \ y = 0,3:\]
\[0,25x \cdot 0,4y = 0,1xy =\]
\[= 0,1 \cdot 1,2 \cdot 0,3 = 0,12 \cdot 0,3 =\]
\[= 0,036.\]
\[3)\ m = 0,22;\ \ n = 100:\]
\[4m \cdot 0,5n = 2mn =\]
\[= 2 \cdot 0,22 \cdot 100 = 2 \cdot 22 = 44.\]
\[4)\ k = 0,58;\ \ c = 0,1:\]
\[0,8\ k \cdot 12,5c = 10kc =\]
\[= 10 \cdot 0,58 \cdot 0,1 = 5,8 \cdot 0,1 =\]
\[= 0,58\]
\[\boxed{\mathbf{929}.\ Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ а)\ n < \frac{206}{13}\text{\ \ }при\ n = 15;\ \ \]
\[так\ как\ \ \frac{206}{13} = \frac{195 + 11}{13} =\]
\[= 15\frac{11}{13}.\]
\[\textbf{б)}\ \frac{324}{16} > n\ \ при\ n = 20;\ \ \]
\[так\ как\ \ \frac{324}{16} = \frac{320 + 4}{16} = 20\frac{4}{16}.\]
\[2)\ а)\ m > \frac{34}{6}\text{\ \ }при\ m = 6;\ \ \]
\[так\ как\ \ \frac{34}{6} = 5\frac{4}{6}.\]
\[\textbf{б)}\ \frac{421}{16} < m\ \ \ при\ m = 27;\ \ \]
\[так\ как\ \ \frac{421}{16} = 26\frac{5}{16}.\]