Решение:

1. $$1\frac{12}{14} + \frac{2}{14} = 1\frac{12+2}{14} = 1\frac{14}{14} = 1 + 1 = 2$$.
2. $$5 - 2\frac{34}{43} = 4\frac{43}{43} - 2\frac{34}{43} = (4-2) + \frac{43-34}{43} = 2\frac{9}{43}$$.
3. $$24\frac{12}{17} - 2\frac{13}{17} = 23\frac{17+12}{17} - 2\frac{13}{17} = 23\frac{29}{17} - 2\frac{13}{17} = 21\frac{29-13}{17} = 21\frac{16}{17}$$.

Ответы: 1) 2; 2) 2\frac{9}{43}; 3) 21\frac{16}{17}