Решение

• a) $$rac{3}{5} + \frac{1}{4} = \frac{3 \cdot 4 + 1 \cdot 5}{5 \cdot 4} = \frac{12 + 5}{20} = \frac{17}{20}$$
• б) $$rac{8}{9} - \frac{1}{3} = \frac{8 - 1 \cdot 3}{9} = \frac{8 - 3}{9} = \frac{5}{9}$$
• в) $$rac{5}{8} + \frac{7}{10} = \frac{5 \cdot 10 + 7 \cdot 8}{8 \cdot 10} = \frac{50 + 56}{80} = \frac{106}{80} = \frac{53}{40} = 1 \frac{13}{40}$$

Ответ:

• a) $$rac{17}{20}$$
• б) $$rac{5}{9}$$
• в) $$1 \frac{13}{40}$$