7. Приведите дроби к общему знаменателю и сложите их: а) 1/4 и 2/3; 2/6 и 2/16; 4/10 и 2/3; 4/30 и 5/12; б) 2/5 и 4/15; 5/42 и 4/6; 3/4 и 1/8.

а)

1. \(\frac{1}{4}+\frac{2}{3}=\frac{3}{12}+\frac{8}{12}=\frac{11}{12}\).
2. Общий знаменатель 24: \(\frac{2}{6}+\frac{2}{16}=\frac{8}{24}+\frac{3}{24}=\frac{11}{24}\).
3. \(\frac{4}{10}+\frac{2}{3}=\frac{6}{15}+\frac{10}{15}=\frac{16}{15}=1\frac{1}{15}\).
4. \(\frac{4}{30}+\frac{5}{12}=\frac{8}{60}+\frac{25}{60}=\frac{33}{60}=\frac{11}{20}\).

б)

1. \(\frac{2}{5}+\frac{4}{15}=\frac{6}{15}+\frac{4}{15}=\frac{10}{15}=\frac{2}{3}\).
2. \(\frac{5}{42}+\frac{4}{6}=\frac{5}{42}+\frac{28}{42}=\frac{33}{42}=\frac{11}{14}\).
3. \(\frac{3}{4}+\frac{1}{8}=\frac{6}{8}+\frac{1}{8}=\frac{7}{8}\).