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30)
$\frac{15}{4} \times \frac{6}{5} = \frac{3 \times 3}{2 \times 1} = \frac{9}{2} = 4 \frac{1}{2}$
31)
$\frac{3}{5} \times \frac{25}{4} = \frac{3 \times 5}{1 \times 4} = \frac{15}{4} = 3 \frac{3}{4}$
32)
$\frac{6}{5} \div \frac{4}{11} = \frac{6}{5} \times \frac{11}{4} = \frac{3 \times 11}{5 \times 2} = \frac{33}{10} = 3 \frac{3}{10}$
33)
$\frac{12}{5} \div \frac{15}{2} = \frac{12}{5} \times \frac{2}{15} = \frac{4 \times 2}{5 \times 5} = \frac{8}{25}$
34)
$\frac{15}{4} \div \frac{3}{7} = \frac{15}{4} \times \frac{7}{3} = \frac{5 \times 7}{4 \times 1} = \frac{35}{4} = 8 \frac{3}{4}$
35)
$\frac{9}{4} + \frac{8}{5} = \frac{45}{20} + \frac{32}{20} = \frac{77}{20} = 3 \frac{17}{20}$
36)
$\frac{11}{4} - \frac{2}{5} = \frac{55}{20} - \frac{8}{20} = \frac{47}{20} = 2 \frac{7}{20}$
37)
$\frac{1}{4} - \frac{3}{25} = \frac{25}{100} - \frac{12}{100} = \frac{13}{100}$