[tex]ex \: 1 \\ \frac{2}{5} + \frac{7}{5} = \frac{9}{5} \\ \\ \frac{10}{21} - \frac{6}{21} = \frac{4}{21} \\ \\ \frac{3}{6} + \frac{4}{12} + \frac{1}{4} = \frac{13}{12} \\ \\ \frac{2}{3} - \frac{1}{5} = \frac{7}{15} \\ \\ \frac{7}{15} + \frac{3}{6} + \frac{2}{5} = \frac{41}{30} \\ \\ \frac{2}{25} \times \frac{7}{5} = \frac{14}{125} \\ \\ 3 \ \frac{2}{5} \times \frac{15}{34} = \frac{3}{2} \\ \\ \frac{24}{5} \div \frac{8}{15} = 9 \\ \\ ( \frac{3}{7} ) {}^{2} = \frac{9}{49} \\ \\ 4 - \frac{3}{8} = \frac{29}{8} [/tex]
[tex]ex \: 3 \\ a) ( 4 \frac{3}{5} - 2 \frac{1}{5} ) \times \frac{5}{6} + 3 = 5 \\ \\ b) \: ( \frac{4}{5} ) {}^{2} \times \frac{20}{8} - \frac{9}{5} \div 3 \frac{6}{10} + \frac{1}{100} = \frac{5}{4} [/tex]
