Упростите выражение: 1) $$\frac{17}{24} c - \frac{5}{24} c$$; 2) $$\frac{7}{18} a + \frac{4}{9} a$$; 3) $$\frac{2}{15} b + \frac{3}{12} b - \frac{7}{20} b$$; 4) $$14 \frac{5}{24} a - 3 \frac{7}{12} a - 5 \frac{9}{16}$$.

1) $$\frac{17}{24} c - \frac{5}{24} c$$ = ($$ \frac{17}{24} - \frac{5}{24}$$) $$\cdot$$ c = $$\frac{12}{24} c$$ = $$\frac{1}{2} c$$

2) $$\frac{7}{18} a + \frac{4}{9} a$$ = ($$\frac{7}{18} + \frac{4}{9}$$) $$\cdot$$ a = ($$\frac{7}{18} + \frac{4 \cdot 2}{9 \cdot 2}$$) $$\cdot$$ a = ($$\frac{7}{18} + \frac{8}{18}$$) $$\cdot$$ a = $$\frac{15}{18} a$$ = $$\frac{5}{6} a$$

3) $$\frac{2}{15} b + \frac{3}{12} b - \frac{7}{20} b$$ = ($$\frac{2}{15} + \frac{1}{4} - \frac{7}{20}$$) $$\cdot$$ b = ($$\frac{2 \cdot 4}{15 \cdot 4} + \frac{1 \cdot 15}{4 \cdot 15} - \frac{7 \cdot 3}{20 \cdot 3}$$) $$\cdot$$ b = ($$\frac{8}{60} + \frac{15}{60} - \frac{21}{60}$$) $$\cdot$$ b = $$\frac{2}{60} b$$ = $$\frac{1}{30} b$$

4) 14$$\frac{5}{24} a - 3 \frac{7}{12} a - 5 \frac{9}{16}$$ = (14$$\frac{5}{24} - 3 \frac{7}{12}$$) $$\cdot$$ a - 5$$\frac{9}{16}$$ = (14$$\frac{5}{24} - 3 \frac{14}{24}$$) $$\cdot$$ a - 5$$\frac{9}{16}$$ = 11$$\frac{-9}{24}$$ a - 5$$\frac{9}{16}$$ = 10$$\frac{15}{24}$$ a - 5$$\frac{9}{16}$$ = 10$$\frac{5}{8}$$ a - 5$$\frac{9}{16}$$

Ответ: 1) $$\frac{1}{2} c$$; 2) $$\frac{5}{6} a$$; 3) $$\frac{1}{30} b$$; 4) 10$$\frac{5}{8}$$ a - 5$$\frac{9}{16}$$