18. Выполните действия: 1) 2/8 + 1/4; 2) 5/7 + 3/5; 3) 8/11 − 1/3; 4) 3/24 + 4/8; 5) 6/12 + 4/18.

1. \(\frac{2}{8}+\frac{1}{4}=\frac{1}{4}+\frac{1}{4}=\frac{1}{2}\).
2. \(\frac{5}{7}+\frac{3}{5}=\frac{25+21}{35}=\frac{46}{35}=1\frac{11}{35}\).
3. \(\frac{8}{11}-\frac{1}{3}=\frac{24-11}{33}=\frac{13}{33}\).
4. \(\frac{3}{24}+\frac{4}{8}=\frac{1}{8}+\frac{1}{2}=\frac{5}{8}\).
5. \(\frac{6}{12}+\frac{4}{18}=\frac{1}{2}+\frac{2}{9}=\frac{13}{18}\).

Ответ: 1/2; 1 11/35; 13/33; 5/8; 13/18.