17. Выполните действие: a) 5/6 + 1/4; б) 7/8 - 5/6; в) 3/10 - 4/15; г) 4/9 * 3/8; д) 5/8 * 9/10; е) 5/9 : 9/10; ж) 2 6/7 : 1 3/7; 3) 6 3/5 * 10.

Решение:

1. a) 5/6 + 1/4
   \( \frac{5}{6} + \frac{1}{4} = \frac{10}{12} + \frac{3}{12} = \frac{13}{12} = 1\frac{1}{12} \)
2. б) 7/8 - 5/6
   \( \frac{7}{8} - \frac{5}{6} = \frac{21}{24} - \frac{20}{24} = \frac{1}{24} \)
3. в) 3/10 - 4/15
   \( \frac{3}{10} - \frac{4}{15} = \frac{9}{30} - \frac{8}{30} = \frac{1}{30} \)
4. г) 4/9 * 3/8
   \( \frac{4}{9} \cdot \frac{3}{8} = \frac{4 \cdot 3}{9 \cdot 8} = \frac{12}{72} = \frac{1}{6} \)
5. д) 5/8 * 9/10
   \( \frac{5}{8} \cdot \frac{9}{10} = \frac{5 \cdot 9}{8 \cdot 10} = \frac{45}{80} = \frac{9}{16} \)
6. е) 5/9 : 9/10
   \( \frac{5}{9} : \frac{9}{10} = \frac{5}{9} \cdot \frac{10}{9} = \frac{50}{81} \)
7. ж) 2 6/7 : 1 3/7
   \( 2\frac{6}{7} : 1\frac{3}{7} = \frac{20}{7} : \frac{10}{7} = \frac{20}{7} \cdot \frac{7}{10} = \frac{20}{10} = 2 \)
8. 3) 6 3/5 * 10
   \( 6\frac{3}{5} \cdot 10 = \frac{33}{5} \cdot 10 = \frac{330}{5} = 66 \)

Ответ: а) 1 1/12; б) 1/24; в) 1/30; г) 1/6; д) 9/16; е) 50/81; ж) 2; 3) 66.