544. Упростите выражение: a) $$ \frac{2}{9}x + \frac{4}{9}x $$; б) $$ \frac{5}{7}a - \frac{9}{14}a $$; в) $$ \frac{7}{12}m - \frac{5}{12}m $$; г) $$ \frac{5}{6}b - \frac{3}{4}b $$; д) $$ 3\frac{1}{6}z + \frac{2}{3}z $$; e) $$ 2\frac{3}{4}t - 1\frac{7}{8}t $$; ж) $$ \frac{2}{3}c + \frac{1}{9}c $$; з) $$ k - \frac{1}{7}k $$; и) $$ \frac{3}{11}y + \frac{8}{11}y $$; к) $$ \frac{3}{5}b + b $$.

a) $$\frac{2}{9}x + \frac{4}{9}x = \frac{2+4}{9}x = \frac{6}{9}x = \frac{2}{3}x$$

б) $$\frac{5}{7}a - \frac{9}{14}a = \frac{5 \cdot 2}{7 \cdot 2}a - \frac{9}{14}a = \frac{10}{14}a - \frac{9}{14}a = \frac{10-9}{14}a = \frac{1}{14}a$$

в) $$\frac{7}{12}m - \frac{5}{12}m = \frac{7-5}{12}m = \frac{2}{12}m = \frac{1}{6}m$$

г) $$\frac{5}{6}b - \frac{3}{4}b = \frac{5 \cdot 2}{6 \cdot 2}b - \frac{3 \cdot 3}{4 \cdot 3}b = \frac{10}{12}b - \frac{9}{12}b = \frac{10-9}{12}b = \frac{1}{12}b$$

д) $$3\frac{1}{6}z + \frac{2}{3}z = \frac{3 \cdot 6 + 1}{6}z + \frac{2}{3}z = \frac{19}{6}z + \frac{2 \cdot 2}{3 \cdot 2}z = \frac{19}{6}z + \frac{4}{6}z = \frac{19+4}{6}z = \frac{23}{6}z = 3\frac{5}{6}z$$

e) $$2\frac{3}{4}t - 1\frac{7}{8}t = \frac{2 \cdot 4 + 3}{4}t - \frac{1 \cdot 8 + 7}{8}t = \frac{11}{4}t - \frac{15}{8}t = \frac{11 \cdot 2}{4 \cdot 2}t - \frac{15}{8}t = \frac{22}{8}t - \frac{15}{8}t = \frac{22-15}{8}t = \frac{7}{8}t$$

ж) $$\frac{2}{3}c + \frac{1}{9}c = \frac{2 \cdot 3}{3 \cdot 3}c + \frac{1}{9}c = \frac{6}{9}c + \frac{1}{9}c = \frac{6+1}{9}c = \frac{7}{9}c$$

з) $$k - \frac{1}{7}k = \frac{7}{7}k - \frac{1}{7}k = \frac{7-1}{7}k = \frac{6}{7}k$$

и) $$\frac{3}{11}y + \frac{8}{11}y = \frac{3+8}{11}y = \frac{11}{11}y = 1y = y$$

к) $$\frac{3}{5}b + b = \frac{3}{5}b + \frac{5}{5}b = \frac{3+5}{5}b = \frac{8}{5}b = 1\frac{3}{5}b$$