3) $\frac{13}{15} + \frac{2}{5} = \frac{13}{15} + \frac{6}{15} = \frac{19}{15} = 1\frac{4}{15}$
4) $2\frac{6}{13} + 1\frac{3}{17} = 3 + \frac{6 \cdot 17 + 3 \cdot 13}{221} = 3 + \frac{102 + 39}{221} = 3\frac{141}{221}$
5) $(\frac{1}{13} + \frac{1}{3}) + \frac{7}{26} = (\frac{3+13}{39}) + \frac{7}{26} = \frac{16}{39} + \frac{7}{26} = \frac{32 + 21}{78} = \frac{53}{78}$
6) $\frac{5}{12} + (3\frac{1}{18} + 2\frac{3}{4}) = \frac{5}{12} + (3\frac{2}{36} + 2\frac{27}{36}) = \frac{5}{12} + 5\frac{29}{36} = \frac{15}{36} + 5\frac{29}{36} = 5\frac{44}{36} = 6\frac{8}{36} = 6\frac{2}{9}$
7) $\frac{45}{7} - \frac{4}{7} = \frac{41}{7} = 5\frac{6}{7}$
8) $\frac{17}{51} - \frac{4}{51} = \frac{13}{51}$
9) $3\frac{1}{15} - 1\frac{2}{5} = 3\frac{1}{15} - 1\frac{6}{15} = 2\frac{16}{15} - 1\frac{6}{15} = 1\frac{10}{15} = 1\frac{2}{3}$
10) $2\frac{1}{13} - 1\frac{4}{17} = \frac{27}{13} - \frac{21}{17} = \frac{459 - 273}{221} = \frac{186}{221}$
11) $\frac{7}{15} + (\frac{8}{9} - \frac{5}{6}) = \frac{7}{15} + (\frac{16}{18} - \frac{15}{18}) = \frac{7}{15} + \frac{1}{18} = \frac{42 + 5}{90} = \frac{47}{90}$
12) $\frac{15}{17} - (\frac{1}{5} + \frac{1}{6}) = \frac{15}{17} - \frac{11}{30} = \frac{450 - 187}{510} = \frac{263}{510}$
13) $2 \cdot \frac{1}{4} = \frac{2}{4} = \frac{1}{2}$
14) $\frac{13}{15} \cdot \frac{1}{39} = \frac{13}{15 \cdot 39} = \frac{1}{15 \cdot 3} = \frac{1}{45}$
15) $\frac{2}{13} \cdot \frac{7}{16} \cdot \frac{13}{7} = \frac{2 \cdot 7 \cdot 13}{13 \cdot 16 \cdot 7} = \frac{2}{16} = \frac{1}{8}$
16) $\frac{7}{12} \cdot \frac{5}{14} + \frac{1}{9} \cdot \frac{3}{8} = \frac{1 \cdot 5}{12 \cdot 2} + \frac{1 \cdot 1}{3 \cdot 8} = \frac{5}{24} + \frac{1}{24} = \frac{6}{24} = \frac{1}{4}$
17) $\frac{21}{22} \cdot (\frac{22}{23} \cdot \frac{24}{25}) \cdot \frac{23}{24} = \frac{21}{22} \cdot \frac{22}{23} \cdot \frac{24}{25} \cdot \frac{23}{24} = \frac{21}{25}$
18) $(47 \cdot \frac{1}{26}) \cdot \frac{13}{27} - (20 \cdot \frac{1}{26}) \cdot \frac{13}{27} = (47-20) \cdot \frac{1}{26} \cdot \frac{13}{27} = 27 \cdot \frac{13}{26 \cdot 27} = \frac{13}{26} = \frac{1}{2}$
19) $2 : \frac{1}{4} = 2 \cdot 4 = 8$
20) $\frac{13}{15} : \frac{1}{8} = \frac{13}{15} \cdot 8 = \frac{104}{15} = 6\frac{14}{15}$
21) $\frac{11}{15} \cdot (\frac{15}{21} : \frac{3}{7}) = \frac{11}{15} \cdot (\frac{15}{21} \cdot \frac{7}{3}) = \frac{11}{15} \cdot (\frac{5}{3} \cdot \frac{1}{1}) = \frac{11}{15} \cdot \frac{5}{3} = \frac{11}{9} = 1\frac{2}{9}$
22) $(\frac{27}{100} : \frac{2}{5}) \cdot \frac{20}{27} = (\frac{27}{100} \cdot \frac{5}{2}) \cdot \frac{20}{27} = \frac{27}{20 \cdot 2} \cdot \frac{20}{27} = \frac{1}{2} \cdot 1 = \frac{1}{2}$
23) $\frac{8}{15} \cdot \frac{1}{2} - \frac{1}{3} : \frac{10}{6} = \frac{4}{15} - (\frac{1}{3} \cdot \frac{6}{10}) = \frac{4}{15} - \frac{2}{10} = \frac{4}{15} - \frac{1}{5} = \frac{4-3}{15} = \frac{1}{15}$
24) $\frac{13}{20} \cdot \frac{1}{2} - \frac{1}{8} : \frac{5}{6} = \frac{13}{40} - (\frac{1}{8} \cdot \frac{6}{5}) = \frac{13}{40} - \frac{3}{20} = \frac{13-6}{40} = \frac{7}{40}$
