Решение:

1. $$1-\frac{13}{55} = \frac{55}{55} - \frac{13}{55} = \frac{55-13}{55} = \frac{42}{55}$$ Ответ:$$\frac{42}{55}$$
2. $$6-\frac{9}{20} = \frac{6*20}{20}-\frac{9}{20} = \frac{120}{20} - \frac{9}{20} = \frac{120-9}{20} = \frac{111}{20} = \frac{5*20+11}{20} = 5\frac{11}{20}$$ Ответ: $$5\frac{11}{20}$$
3. $$10-5\frac{12}{35} = 10 - \frac{5*35+12}{35} = 10 - \frac{175+12}{35} = 10 - \frac{187}{35} = \frac{10*35}{35} - \frac{187}{35} = \frac{350-187}{35} = \frac{163}{35} = \frac{4*35+23}{35} = 4\frac{23}{35}$$ Ответ: $$4\frac{23}{35}$$