1. Вычислите: a) 10\frac{4}{15}+9\frac{11}{15}-8\frac{1}{30}; б) 19\frac{1}{17}-8\frac{9}{17}-3\frac{15}{17}; в) (6\frac{7}{12}+8\frac{5}{12})-7\frac{16}{21}-4\frac{6}{21};

a) Вычислим:

$$10\frac{4}{15}+9\frac{11}{15}-8\frac{1}{30}=10\frac{8}{30}+9\frac{22}{30}-8\frac{1}{30}=19\frac{30}{30}-8\frac{1}{30}=19+1-8\frac{1}{30}=20-8\frac{1}{30}=11\frac{29}{30}$$.

Ответ: $$11\frac{29}{30}$$

б) Вычислим:

$$19\frac{1}{17}-8\frac{9}{17}-3\frac{15}{17}=19\frac{1}{17}-(8\frac{9}{17}+3\frac{15}{17})=19\frac{1}{17}-11\frac{24}{17}=19\frac{1}{17}-12\frac{7}{17}=6\frac{18}{17}-12\frac{7}{17}=6\frac{18-7}{17}=6\frac{11}{17}$$.

Ответ: $$6\frac{11}{17}$$

в) Вычислим:

$$(6\frac{7}{12}+8\frac{5}{12})-7\frac{16}{21}-4\frac{6}{21}=14\frac{12}{12}-7\frac{16}{21}-4\frac{6}{21}=15-7\frac{16}{21}-4\frac{6}{21}=15-(7\frac{16}{21}+4\frac{6}{21})=15-11\frac{22}{21}=15-12\frac{1}{21}=14\frac{21}{21}-12\frac{1}{21}=2\frac{20}{21}$$.

Ответ: $$2\frac{20}{21}$$