3\4+4\5+1\20 3\4+5\12+1\9 7\15-(2\15+1\5) 3\16+(15\16-5\8)

Решите задачу:

$\frac{3}{4} + \frac{4}{5} + \frac{1}{20} = \frac{3}{4} + \frac{4}{5} + \frac{1}{4*5}= \frac{3*5}{4*5} + \frac{4*4}{5*4} + \frac{1}{4*5}= \frac{15}{20} + \frac{16}{20} + \frac{1}{20}= \frac{32}{20} = \\ =\frac{8}{5} =1 \frac{3}{5} ; \\ \frac{3}{4}+ \frac{5}{12}+ \frac{1}{9}= \frac{3}{4}+ \frac{5}{4*3}+ \frac{1}{3*3}= \frac{3*9}{4*9}+ \frac{5*3}{4*3*3}+ \frac{1*4}{3*3*4}= \\ = \frac{27}{36}+ \frac{15}{36}+ \frac{4}{36}= \frac{46}{36} = \frac{23}{18}=1 \frac{5}{18}; \\$

$\frac{7}{15}-( \frac{2}{15} + \frac{1}{5} )=\frac{7}{15}-\frac{2}{15} - \frac{1}{5} = \frac{5}{15} - \frac{1}{5}=\frac{5}{5*3} - \frac{1*3}{5*3}=\frac{5}{15} - \frac{3}{15}= \\ = \frac{2}{15} ; \\ \frac{3}{16}+( \frac{15}{16} - \frac{5}{8} )=\frac{3}{16}+ \frac{15}{16} - \frac{5}{8} = \frac{18}{16} - \frac{5}{8} =\frac{18}{16} - \frac{10}{16} = \frac{8}{16}= \frac{1}{2}$