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Решите задачу:

$1.\tt\displaystyle\frac{21}{35}:\frac{24}{60}=\frac{21}{35}*\frac{60}{24}=\frac{21:7}{35:7}*\frac{60:12}{24:12}=\frac{3}{5}*\frac{5}{2}=\frac{3}{2}=1\frac{1}{2}$

$2.(3\tt\displaystyle\frac{11}{27}-2\frac{17}{18}):1\frac{23}{27}+3\frac{3}{5}:3=1\frac{9}{20}$

$1)3\tt\displaystyle\frac{11}{27}-2\frac{17}{18}=\frac{3*27+11}{27}-\frac{2*18+17}{18}=\frac{92}{27}-\frac{53}{18}=\frac{92*2}{27*2}-\frac{53*3}{18*3}=\frac{184}{54}-\frac{159}{54}=\frac{25}{54}$

$2)\tt\displaystyle\frac{25}{54}:1\frac{23}{27}=\frac{25}{54}:\frac{50}{27}=\frac{25}{54}*\frac{27}{50}=\frac{1}{4}$

$3)3\tt\displaystyle\frac{3}{5}:3=\frac{3*5+3}{5}:3=\frac{18}{5}*\frac{1}{3}=\frac{6}{5}$

$4)\tt\displaystyle\frac{1}{4}+\frac{6}{5}=\frac{1*5}{4*5}+\frac{6*4}{5*4}=\frac{5}{20}+\frac{24}{20}=\frac{29}{20}=1\frac{9}{20}$