2. Выполните действия 5 a) 9+18 17 5 6) 20 12 B) 15 10 45 r)7-4음 д) 40+1름

2. Выполните действия

a) $$ \frac{2}{9} + \frac{5}{18} = \frac{2 \cdot 2}{9 \cdot 2} + \frac{5}{18} = \frac{4}{18} + \frac{5}{18} = \frac{4 + 5}{18} = \frac{9}{18} = \frac{1}{2} $$

б) $$ \frac{17}{20} - \frac{5}{12} = \frac{17 \cdot 3}{20 \cdot 3} - \frac{5 \cdot 5}{12 \cdot 5} = \frac{51}{60} - \frac{25}{60} = \frac{51 - 25}{60} = \frac{26}{60} = \frac{13}{30} $$

в) $$ \frac{11}{15} - \frac{3}{10} + \frac{1}{45} = \frac{11 \cdot 6}{15 \cdot 6} - \frac{3 \cdot 9}{10 \cdot 9} + \frac{1 \cdot 2}{45 \cdot 2} = \frac{66}{90} - \frac{27}{90} + \frac{2}{90} = \frac{66 - 27 + 2}{90} = \frac{41}{90} $$

г) $$ 7 - 4 \frac{5}{9} = 6 \frac{9}{9} - 4 \frac{5}{9} = (6 - 4) + (\frac{9}{9} - \frac{5}{9}) = 2 + \frac{4}{9} = 2 \frac{4}{9} $$

д) $$ 4 \frac{3}{10} + 1 \frac{5}{12} = 4 + \frac{3}{10} + 1 + \frac{5}{12} = (4 + 1) + (\frac{3}{10} + \frac{5}{12}) = 5 + (\frac{3 \cdot 6}{10 \cdot 6} + \frac{5 \cdot 5}{12 \cdot 5}) = 5 + (\frac{18}{60} + \frac{25}{60}) = 5 + \frac{43}{60} = 5 \frac{43}{60} $$

Ответ: a) $$\frac{1}{2}$$, б) $$\frac{13}{30}$$, в) $$\frac{41}{90}$$, г) $$2 \frac{4}{9}$$, д) $$5 \frac{43}{60}$$