Вычислите: а) \(\frac{9}{19}+\frac{4}{9}\); б) \(\left(2-1\frac{11}{21}\right)-1\frac{2}{3}\); в) \(-5\frac{7}{8}-12+4\frac{5}{8}=-3,5\).

а) \[\frac{9}{19}+\frac{4}{9}=\frac{81}{171}+\frac{76}{171}=\frac{157}{171}.\]

б) \[2-1\frac{11}{21}=\frac{42}{21}-\frac{32}{21}=\frac{10}{21},\qquad 1\frac{2}{3}=\frac{35}{21}.\] Тогда \[\frac{10}{21}-\frac{35}{21}=-\frac{25}{21}=-1\frac{4}{21}.\]

в) \[-5\frac{7}{8}-12+4\frac{5}{8}=-5\frac{7}{8}+4\frac{5}{8}-12=-1\frac{1}{4}-12=-13\frac{1}{4}.\] Это не равно \(-3,5
");