\[\boxed{\mathbf{484\ (484).}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ \frac{2a}{21}\ :\frac{4b}{49} = \frac{2a \cdot 49}{21 \cdot 4b} = \frac{a \cdot 7}{3 \cdot 2b} =\]
\[= \frac{7a}{6b}\]
\[2)\ \frac{11m}{9n}\ :\frac{22n}{27m} = \frac{11m \cdot 27m}{9n \cdot 22n} =\]
\[= \frac{m \cdot 3m}{n \cdot 2n} = \frac{3m^{2}}{2n^{2}}\]
\[3)\ \frac{36ab}{17c}\ :\frac{21b}{34c} = \frac{36ab}{17c} \cdot \frac{34c}{21b} =\]
\[= \frac{36ab \cdot 34c}{17c \cdot 21b} = \frac{12a \cdot 2}{1 \cdot 7} = \frac{24a}{7}\]
\[4)\ \frac{51x}{32y}\ :\frac{17x}{16y} = \frac{51x}{32y} \cdot \frac{16y}{17x} =\]
\[= \frac{51x \cdot 16y}{32y \cdot 17x} = \frac{3 \cdot 1}{2 \cdot 1} = \frac{3}{2} = 1\frac{1}{2}\]
\[\boxed{\mathbf{484}.}\]
\[0,205 < 0,25 < 0,502 < 0,52.\]
\[M(0,205);N(0,25);K(0,502);P(0,52).\]