tính nhanh : 3/11x7/19+17/11x3/19-3/9x25/11
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![](https://rs.olm.vn/images/avt/0.png?1311)
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3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19
= (3 + 19) + (5 + 17) + (7 + 15) + (9 + 13) + 11
= 22 + 22 + 22 + 22 + 11
= 22 x 4 + 11
= 88 + 11
= 99
![](https://rs.olm.vn/images/avt/0.png?1311)
\(M=\frac{75-\frac{6}{13}+\frac{3}{17}-\frac{3}{19}}{275-\frac{22}{13}+\frac{11}{17}-\frac{11}{19}}\)
\(=\frac{3.25-\frac{2}{13}+\frac{1}{17}-\frac{1}{19}}{11.25-\frac{2}{13}+\frac{1}{17}-\frac{1}{19}}\)
\(=\frac{3}{11}\)
Vậy: \(M=\frac{3}{11}\)
75-3(2/13+1/17-3/19) 75-3 72 3
-------------------------------------------------=------- =-------=----
275-11(2/13+1/17-1/19 275-11 264 11
![](https://rs.olm.vn/images/avt/0.png?1311)
=43/306:599/105x1473/1820
=1505/61098x1473/1820
=0.01993613035
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
=19-17+15-13+11-9+7-5+3-1
=2+2+2+2+2
=10
Hay nói cách khác là:
2*5=10