I B. 1) 1/9 + 2/3 ) 7/8 - 1/3 ) 2 1/5 + 3/4 -1 3/4

Решение:

1. $$ \frac{1}{9} + \frac{2}{3} = \frac{1}{9} + \frac{2 \cdot 3}{3 \cdot 3} = \frac{1}{9} + \frac{6}{9} = \frac{1+6}{9} = \frac{7}{9} $$
2. $$ \frac{7}{8} - \frac{1}{3} = \frac{7 \cdot 3}{8 \cdot 3} - \frac{1 \cdot 8}{3 \cdot 8} = \frac{21}{24} - \frac{8}{24} = \frac{21-8}{24} = \frac{13}{24} $$
3. $$ 2 \frac{1}{5} + \frac{3}{4} = \frac{2 \cdot 5 + 1}{5} + \frac{3}{4} = \frac{11}{5} + \frac{3}{4} = \frac{11 \cdot 4}{5 \cdot 4} + \frac{3 \cdot 5}{4 \cdot 5} = \frac{44}{20} + \frac{15}{20} = \frac{44+15}{20} = \frac{59}{20} = 2 \frac{19}{20} $$
4. $$ -1 \frac{3}{4} = - \frac{1 \cdot 4 + 3}{4} = - \frac{7}{4} = -1.75 $$

Ответ:

1. 7/9
2. 13/24
3. 2 19/20
4. -1 3/4 = -7/4 = -1.75