№2. Найдите значения выражений: 1) 7/16 * 8/21; 5) -5 1/3 - 1 1/2; 9) 31 1/2 : 2 1/31; 2) -5/11 - 33/65; 6) -3 1/7 - 1 3/11; 10) 5/9 * (-9); 3) 19/23 * (-46/57); 7) 5/7 : (-10/21); 4) 3 1/4 * 3 9/13; 8) -4/5 : (-1 1/15); 13) 6,5 - 2,6; 14) -5,3 * 7,7; 15) -6,4 * (-1,3); 16) 0,81 : 0,009; 17) 0,1515 : 0,05; 12) -14 : (-2 4/5); 18) 0,361 : 0,19;

Решение:

1. \( \frac{7}{16} \cdot \frac{8}{21} = \frac{7 \cdot 8}{16 \cdot 21} = \frac{1 \cdot 1}{2 \cdot 3} = \frac{1}{6} \)
2. \( -\frac{5}{11} - \frac{33}{65} = -\frac{5 \cdot 65 + 33 \cdot 11}{11 \cdot 65} = -\frac{325 + 363}{715} = -\frac{688}{715} \)
3. \( \frac{19}{23} \cdot \left(-\frac{46}{57}\right) = \frac{19}{23} \cdot \left(-\frac{2 \cdot 23}{3 \cdot 19}\right) = -\frac{2}{3} \)
4. \( 3\frac{1}{4} \cdot 3\frac{9}{13} = \frac{13}{4} \cdot \frac{48}{13} = \frac{13 \cdot 48}{4 \cdot 13} = 12 \)
5. \( -5\frac{1}{3} - 1\frac{1}{2} = -\frac{16}{3} - \frac{3}{2} = -\frac{32}{6} - \frac{9}{6} = -\frac{41}{6} = -6\frac{5}{6} \)
6. \( -3\frac{1}{7} - 1\frac{3}{11} = -\frac{22}{7} - \frac{14}{11} = -\frac{242}{77} - \frac{98}{77} = -\frac{340}{77} = -4\frac{32}{77} \)
7. \( \frac{5}{7} : \left(-\frac{10}{21}\right) = \frac{5}{7} \cdot \left(-\frac{21}{10}\right) = -\frac{5 \cdot 21}{7 \cdot 10} = -\frac{1 \cdot 3}{1 \cdot 2} = -\frac{3}{2} = -1\frac{1}{2} \)
8. \( -\frac{4}{5} : \left(-1\frac{1}{15}\right) = -\frac{4}{5} : \left(-\frac{16}{15}\right) = \frac{4}{5} \cdot \frac{15}{16} = \frac{4 \cdot 15}{5 \cdot 16} = \frac{1 \cdot 3}{1 \cdot 4} = \frac{3}{4} \)
9. \( 31\frac{1}{2} : 2\frac{1}{31} = \frac{63}{2} : \frac{63}{31} = \frac{63}{2} \cdot \frac{31}{63} = \frac{31}{2} = 15\frac{1}{2} \)
10. \( \frac{5}{9} \cdot (-9) = -5 \)
11. \( -\frac{4}{5} : 9 = -\frac{4}{45} \)
12. \( -14 : \left(-2\frac{4}{5}\right) = -14 : \left(-\frac{14}{5}\right) = 14 \cdot \frac{5}{14} = 5 \)
13. \( 6,5 - 2,6 = 3,9 \)
14. \( -5,3 \cdot 7,7 = -40,81 \)
15. \( -6,4 \cdot (-1,3) = 8,32 \)
16. \( 0,81 : 0,009 = 90 \)
17. \( 0,1515 : 0,05 = 3,03 \)
18. \( 0,361 : 0,19 = 1,9 \)