Решение:

12. a)

$$ 1 \frac{9}{11} + 2 \frac{3}{11} = (1+2) + (\frac{9}{11} + \frac{3}{11}) = 3 + \frac{12}{11} = 3 + 1 \frac{1}{11} = 4 \frac{1}{11} $$

12. б)

$$ 3 \frac{2}{9} + 1 \frac{7}{9} = (3+1) + (\frac{2}{9} + \frac{7}{9}) = 4 + \frac{9}{9} = 4 + 1 = 5 $$

12. в)

$$ 4 \frac{1}{3} - 2 \frac{2}{3} = \frac{13}{3} - \frac{8}{3} = \frac{13-8}{3} = \frac{5}{3} = 1 \frac{2}{3} $$

12. г)

$$ 26 \frac{2}{5} - 17 \frac{3}{5} = 25 \frac{7}{5} - 17 \frac{3}{5} = (25-17) + (\frac{7}{5} - \frac{3}{5}) = 8 + \frac{4}{5} = 8 \frac{4}{5} $$

12. д)

$$ 8 \frac{2}{7} - 3 \frac{4}{7} = 7 \frac{9}{7} - 3 \frac{4}{7} = (7-3) + (\frac{9}{7} - \frac{4}{7}) = 4 + \frac{5}{7} = 4 \frac{5}{7} $$

Ответ:

• a) $$4 \frac{1}{11}$$
• б) $$5$$
• в) $$1 \frac{2}{3}$$
• г) $$8 \frac{4}{5}$$
• д) $$4 \frac{5}{7}$$