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1. $ 6×(-1.2)×5= $______
答案
-36
解析
$6×(-1.2)×5$
$=6×5×(-1.2)$
$=30×(-1.2)$
$=-36$
$=6×5×(-1.2)$
$=30×(-1.2)$
$=-36$
2. $ (-6)×5×(-\frac {7}{6})= $______
答案
35
解析
$(-6) × 5 × \left(-\frac{7}{6}\right)$
$=(-6) × \left(-\frac{7}{6}\right) × 5$
$=7 × 5$
$=35$
$=(-6) × \left(-\frac{7}{6}\right) × 5$
$=7 × 5$
$=35$
3. $ -2.1×5.4×(-\frac {1}{7})= $______
答案
1.62
解析
$-2.1×5.4×(-\frac{1}{7})$
$=(-2.1)×(-\frac{1}{7})×5.4$
$=0.3×5.4$
$=1.62$
$=(-2.1)×(-\frac{1}{7})×5.4$
$=0.3×5.4$
$=1.62$
4. $ (-7)×(-\frac {4}{3})×\frac {5}{14}= $______
答案
$\frac{10}{3}$
解析
$(-7)×(-\frac{4}{3})×\frac{5}{14}$
$=7×\frac{4}{3}×\frac{5}{14}$
$=7×\frac{5}{14}×\frac{4}{3}$
$=\frac{5}{2}×\frac{4}{3}$
$=\frac{10}{3}$
$=7×\frac{4}{3}×\frac{5}{14}$
$=7×\frac{5}{14}×\frac{4}{3}$
$=\frac{5}{2}×\frac{4}{3}$
$=\frac{10}{3}$
5. $ 2.5×(-5)×(-7)×4= $_____
答案
350
解析
$2.5×(-5)×(-7)×4$
$=2.5×4×(-5)×(-7)$
$=10×35$
$=350$
$=2.5×4×(-5)×(-7)$
$=10×35$
$=350$
6. $ (-18)×3.17-3.17×82= $______
答案
-317
解析
$(-18) × 3.17 - 3.17 × 82$
$=3.17 × (-18 - 82)$
$=3.17 × (-100)$
$=-317$
$=3.17 × (-18 - 82)$
$=3.17 × (-100)$
$=-317$
7. $ (-25)×(-32)$
答案
800
解析
$(-25)×(-32)$
$=25×32$
$=25×4×8$
$=100×8$
$=800$
$=25×32$
$=25×4×8$
$=100×8$
$=800$
8. $ (-5)×(+19)-(-5)×9$
答案
-50
解析
$(-5) × (+19) - (-5) × 9$
$= (-5) × (19 - 9)$
$= (-5) × 10$
$= -50$
$= (-5) × (19 - 9)$
$= (-5) × 10$
$= -50$
9. $ (-16)×(-\frac {1}{8}+\frac {3}{4}-1\frac {1}{2})$
答案
14
解析
$(-16)×(-\frac{1}{8}+\frac{3}{4}-1\frac{1}{2})$
$=(-16)×(-\frac{1}{8})+(-16)×\frac{3}{4}-(-16)×\frac{3}{2}$
$=2-12+24$
$=14$
$=(-16)×(-\frac{1}{8})+(-16)×\frac{3}{4}-(-16)×\frac{3}{2}$
$=2-12+24$
$=14$
10. $ \frac {15}{31}×(-\frac {2}{9})×(-2\frac {1}{15})×(-4\frac {1}{2})$
答案
-1
解析
$\frac{15}{31} × (-\frac{2}{9}) × (-2\frac{1}{15}) × (-4\frac{1}{2})$
$=\frac{15}{31} × (-\frac{2}{9}) × (-\frac{31}{15}) × (-\frac{9}{2})$
$=-\left(\frac{15}{31} × \frac{31}{15}\right) × \left(\frac{2}{9} × \frac{9}{2}\right)$
$=-1×1$
$=-1$
$=\frac{15}{31} × (-\frac{2}{9}) × (-\frac{31}{15}) × (-\frac{9}{2})$
$=-\left(\frac{15}{31} × \frac{31}{15}\right) × \left(\frac{2}{9} × \frac{9}{2}\right)$
$=-1×1$
$=-1$
11. $ 25×\frac {1}{5}+25×\frac {1}{10}-25×\frac {1}{2}$
答案
-5
解析
$25×\frac{1}{5} + 25×\frac{1}{10} - 25×\frac{1}{2}$
$=25×\left(\frac{1}{5}+\frac{1}{10}-\frac{1}{2}\right)$
$=25×\left(\frac{2}{10}+\frac{1}{10}-\frac{5}{10}\right)$
$=25×\left(-\frac{2}{10}\right)$
$=25×\left(-\frac{1}{5}\right)$
$=-5$
$=25×\left(\frac{1}{5}+\frac{1}{10}-\frac{1}{2}\right)$
$=25×\left(\frac{2}{10}+\frac{1}{10}-\frac{5}{10}\right)$
$=25×\left(-\frac{2}{10}\right)$
$=25×\left(-\frac{1}{5}\right)$
$=-5$
12. $ (-60)×(\frac {2}{3}-\frac {1}{10}-\frac {2}{5}+\frac {1}{6})$
答案
-20
解析
$(-60) × \left( \frac{2}{3} - \frac{1}{10} - \frac{2}{5} + \frac{1}{6} \right)$
$= (-60) × \frac{2}{3} + (-60) × \left( -\frac{1}{10} \right) + (-60) × \left( -\frac{2}{5} \right) + (-60) × \frac{1}{6}$
$= -40 + 6 + 24 - 10$
$= -20$
$= (-60) × \frac{2}{3} + (-60) × \left( -\frac{1}{10} \right) + (-60) × \left( -\frac{2}{5} \right) + (-60) × \frac{1}{6}$
$= -40 + 6 + 24 - 10$
$= -20$
13. $ (-\frac {1}{2}×\frac {3}{2})×(-\frac {2}{3}×\frac {4}{3})×(-\frac {3}{4}×\frac {5}{4})×... ×(-\frac {213}{214}×\frac {215}{214})×(-\frac {214}{215}×\frac {216}{215})$
答案
$\frac{108}{215}$
解析
$(-\frac{1}{2}×\frac{3}{2})×(-\frac{2}{3}×\frac{4}{3})×(-\frac{3}{4}×\frac{5}{4})×...×(-\frac{214}{215}×\frac{216}{215})$
$=(-1)^{214}×(\frac{1}{2}×\frac{2}{3}×\frac{3}{4}×...×\frac{214}{215})×(\frac{3}{2}×\frac{4}{3}×\frac{5}{4}×...×\frac{216}{215})$
$=1×\frac{1}{215}×\frac{216}{2}$
$=\frac{108}{215}$
$=(-1)^{214}×(\frac{1}{2}×\frac{2}{3}×\frac{3}{4}×...×\frac{214}{215})×(\frac{3}{2}×\frac{4}{3}×\frac{5}{4}×...×\frac{216}{215})$
$=1×\frac{1}{215}×\frac{216}{2}$
$=\frac{108}{215}$
