1. Найдите значение выражения 1) 19/28 + 16/28 - 17/28; 2) 11/14 - 5/14 + 3/14; 3) 1 - 8/17; 4) 5/9 * 8/9; 5) 4/9 * 5/8; 6) 8/13 : 4; 7) 3/8 * 1/5 * 19/20

Решение:

• 1) \( \frac{19}{28} + \frac{16}{28} - \frac{17}{28} = \frac{19+16-17}{28} = \frac{18}{28} = \frac{9}{14} \)
• 2) \( \frac{11}{14} - \frac{5}{14} + \frac{3}{14} = \frac{11-5+3}{14} = \frac{9}{14} \)
• 3) \( 1 - \frac{8}{17} = \frac{17}{17} - \frac{8}{17} = \frac{17-8}{17} = \frac{9}{17} \)
• 4) \( \frac{5}{9} \cdot \frac{8}{9} = \frac{5 \cdot 8}{9 \cdot 9} = \frac{40}{81} \)
• 5) \( \frac{4}{9} \cdot \frac{5}{8} = \frac{4 \cdot 5}{9 \cdot 8} = \frac{20}{72} = \frac{5}{18} \)
• 6) \( \frac{8}{13} : 4 = \frac{8}{13} : \frac{4}{1} = \frac{8}{13} \cdot \frac{1}{4} = \frac{8 \cdot 1}{13 \cdot 4} = \frac{8}{52} = \frac{2}{13} \)
• 7) \( \frac{3}{8} \cdot \frac{1}{5} \cdot \frac{19}{20} = \frac{3 \cdot 1 \cdot 19}{8 \cdot 5 \cdot 20} = \frac{57}{800} \)

Ответ: 1) 9/14; 2) 9/14; 3) 9/17; 4) 40/81; 5) 5/18; 6) 2/13; 7) 57/800