15. Вычислите: 1) 18 2/4 + 4 1/4; 2) 12 5/7 − 1 4/7; 3) 8 − 2/3; 4) 5 2/9 − 1 3/9; 5) 20 7/17 − 5 2/17; 6) 12 − 2 3/4.

1. \(18\frac{2}{4}+4\frac{1}{4}=22\frac{3}{4}\).
2. \(12\frac{5}{7}-1\frac{4}{7}=11\frac{1}{7}\).
3. \(8-\frac{2}{3}=7\frac{1}{3}\).
4. \(5\frac{2}{9}-1\frac{3}{9}=3\frac{8}{9}\).
5. \(20\frac{7}{17}-5\frac{2}{17}=15\frac{5}{17}\).
6. \(12-2\frac{3}{4}=9\frac{1}{4}\).

Ответ: 22\(\frac{3}{4}\); 11\(\frac{1}{7}\); 7\(\frac{1}{3}\); 3\(\frac{8}{9}\); 15\(\frac{5}{17}\); 9\(\frac{1}{4}\).