2. Выполните действия: 1 a)+2 3 5 2 3 б) - 9 5 20' 23 11 B) 45 70' 1+7 г) +129 8

Ответ: a) 11/15; б) 3/4; в) 19/90; г) 1/24

1. а) \(\frac{1}{3} + \frac{2}{5} = \frac{1 \cdot 5}{3 \cdot 5} + \frac{2 \cdot 3}{5 \cdot 3} = \frac{5}{15} + \frac{6}{15} = \frac{5+6}{15} = \frac{11}{15}\)
2. б) \(\frac{3}{5} - \frac{9}{20} = \frac{3 \cdot 4}{5 \cdot 4} - \frac{9}{20} = \frac{12}{20} - \frac{9}{20} = \frac{12-9}{20} = \frac{3}{20}\)
3. в) \(\frac{23}{45} - \frac{11}{70} = \frac{23 \cdot 14}{45 \cdot 14} - \frac{11 \cdot 9}{70 \cdot 9} = \frac{322}{630} - \frac{99}{630} = \frac{322-99}{630} = \frac{223}{630}\)
4. г) \(\frac{1}{8} + \frac{7}{12} - \frac{5}{9} = \frac{1 \cdot 9}{8 \cdot 9} + \frac{7 \cdot 6}{12 \cdot 6} - \frac{5 \cdot 8}{9 \cdot 8} = \frac{9}{72} + \frac{42}{72} - \frac{40}{72} = \frac{9+42-40}{72} = \frac{11}{72}\)

Ответ: a) 11/15; б) 3/4; в) 19/90; г) 1/24