1) 2/3 + 5/8 4) 6/35 + 3/10 7) 11/48 - 3/36

Решение:

1. 1)
   \[ \frac{2}{3} + \frac{5}{8} = \frac{16+15}{24} = \frac{31}{24} \]
2. 4)
   \[ \frac{6}{35} + \frac{3}{10} = \frac{12+21}{70} = \frac{33}{70} \]
3. 7)
   \[ \frac{11}{48} - \frac{3}{36} = \frac{11}{48} - \frac{1}{12} = \frac{11-4}{48} = \frac{7}{48} \]

Ответ: 1) 31/24; 4) 33/70; 7) 7/48