2. Найдите значение выражения: 1) 7+5.31+9+13,49; 2) 62.7+8.31+5.79+0.07; 3)8.31-(4.29+3,721); 4) (8.21+9,73)-0,001; 5) 3:1\(\frac{1}{2}\)+5:1\(\frac{1}{4}\); 6) 10\(\frac{2}{3}\)-5\(\frac{1}{3}\)\(\cdot\)\(\frac{3}{5}\); 7) \(10\frac{2}{5}-5\frac{1}{3}\):1\(\frac{3}{5}\); 8) 4\(\frac{1}{2}\) - 5\(\frac{1}{9}\):10\(\frac{2}{3}\); 9) 0,7·1,3+5,1:0,17; 10) 3,38-2,24:1,25; 11) (3,38-2,24):1,25; 12) 31,7:63,4-23,4:11,7;

Решение:

1. \( 7+5.31+9+13.49 = 34.8 \)


2. \( 62.7+8.31+5.79+0.07 = 76.87 \)


3. \( 8.31-(4.29+3.721) = 8.31-8.011 = 0.299 \)


4. \( (8.21+9.73)-0.001 = 17.94-0.001 = 17.939 \)


5. \( 3:\frac{3}{2}+5:\frac{5}{4} = 3 \cdot \frac{2}{3} + 5 \cdot \frac{4}{5} = 2+4 = 6 \)


6. \( 10\frac{2}{3}-5\frac{1}{3} \cdot \frac{3}{5} = \frac{32}{3} - \frac{16}{3} \cdot \frac{3}{5} = \frac{32}{3} - \frac{16}{5} = \frac{160-48}{15} = \frac{112}{15} = 7\frac{7}{15} \)


7. \( (10\frac{2}{5}-5\frac{1}{3}):1\frac{3}{5} = (\frac{52}{5} - \frac{16}{3}) : \frac{8}{5} = (\frac{156-80}{15}) : \frac{8}{5} = \frac{76}{15} \cdot \frac{5}{8} = \frac{76}{3 \cdot 8} = \frac{19}{6} = 3\frac{1}{6} \)


8. \( 4\frac{1}{2} - 5\frac{1}{9}:10\frac{2}{3} = \frac{9}{2} - \frac{46}{9} : \frac{32}{3} = \frac{9}{2} - \frac{46}{9} \cdot \frac{3}{32} = \frac{9}{2} - \frac{46}{3 \cdot 32} = \frac{9}{2} - \frac{23}{48} = \frac{9 \cdot 24 - 23}{48} = \frac{216-23}{48} = \frac{193}{48} = 4\frac{1}{48} \)


9. \( 0.7 \cdot 1.3 + 5.1:0.17 = 0.91 + 30 = 30.91 \)


10. \( 3.38 - 2.24:1.25 = 3.38 - 1.792 = 1.588 \)


11. \( (3.38-2.24):1.25 = 1.14:1.25 = 0.912 \)


12. \( 31.7:63.4-23.4:11.7 = 0.5-2 = -1.5 \)

Ответ: 1) 34.8; 2) 76.87; 3) 0.299; 4) 17.939; 5) 6; 6) 7\(\frac{7}{15}\); 7) 3\(\frac{1}{6}\); 8) 4\(\frac{1}{48}\); 9) 30.91; 10) 1.588; 11) 0.912; 12) -1.5.