Алгебра! Срочно нужно! Даю 30 баллов!

Объяснение:

$\frac{21}{5} \div \frac{6}{7} = \frac{21 \times 7}{5 \times 6} = \frac{7 \times 7}{5 \times 2} = \frac{49}{10} = 4.9$

$\frac{3}{5} \div \frac{4}{35} = \frac{3 \times 35}{5 \times 4} = \frac{3 \times 7}{4} = \frac{21}{4} = 5 \frac{1}{4} = 5.25$

$\frac{4}{5} \div \frac{2}{7} = \frac{4 \times 7}{5 \times 2} = \frac{14}{5} = 2 \frac{4}{5} = 2.8$

$\frac{21}{2} \div \frac{3}{5 } = \frac{21 \times 5}{2 \times 3} = \frac{35}{2} = 17 \frac{1}{2} = 17.5$

$\frac{3}{4} + \frac{7}{25} = \frac{3 \times 25 + 7 \times 4}{100} = \frac{75 + 28}{100} = \frac{103}{100} = 1 \frac{3}{100} = 1.03$

$\frac{9}{4} + \frac{8}{5} = 2 \frac{1}{4} + 1 \frac{3}{5} = 3 \frac{5 + 12}{20} = 3 \frac{17}{20} = 3.85$

$\frac{11}{5} + \frac{13}{4} = 2 \frac{1}{5} + 3 \frac{1}{4} = 5 \frac{4 + 5}{20} = 5 \frac{9}{20} = 5.45$