Tính bằng cách thuận tiện . 3×7/10+7/10×5+2×14/20
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3 x 7/10 + 7/10 x 5 + 2 x 7/10
= 7/10 x (3 + 5 + 2)
= 7/10 x 10
= 7
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{7}{10}\times\left(3+5+2\right)=\dfrac{7}{10}\times10=\dfrac{70}{10}=7\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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10/7+9/27+8/14+5/3
=10/7+1/3+4/7+5/3
=(10/7+4/7)+(1/3+5/3)
=14/7+6/3
=2+2
=4
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}\)
\(=\frac{1.3.5\left(1+2+4+7\right)}{1.5.7\left(1+2+7+7\right)}=\frac{1.3.5}{1.5.7}=\frac{15}{35}=\frac{3}{7}\)
\(\frac{1\cdot3\cdot5+2\cdot6\cdot10+4\cdot12\cdot20+7\cdot21\cdot35}{1\cdot5\cdot7+2\cdot10\cdot14+4\cdot20\cdot28+7\cdot35\cdot49}\)
\(=\)\(\frac{1\cdot3\cdot5\cdot\left(1+2+4+7\right)}{1\cdot5\cdot7\cdot\left(1+2+7+7\right)}\)
\(=\frac{1\cdot3\cdot5}{1\cdot5\cdot7}\)\(=\frac{15}{35}=\frac{3}{7}\)
bn vội quá viết nhầm lun kìa
hj hj chúc bn làm bài tốt nha
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1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10
=20+20+20+20+20+20+20+20+20+20+10
=20×10+10
=200+10
=210
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20
= 20 + 20 + 20 +20 + 20 +20 + 20 + 20 + 20 +20
= 20 x 10
= 200
tui đầu tiên đó
![](https://rs.olm.vn/images/avt/0.png?1311)
3 x 7/10 + 7/10 x 5 + 2 x 14/20
=3x7/10+7/10x5+2x7/10
=7/10x(3+5+2)
=7/10x10
=7
ta có
\(3\cdot\frac{7}{10}+\frac{7}{10}\cdot5+2\cdot\frac{14}{20}\)
\(=3\cdot\frac{7}{10}+\frac{7}{10}\cdot5+2\cdot\frac{7}{10}\)
\(=\frac{7}{10}\cdot\left(3+5+2\right)\)
\(=\frac{7}{10}\cdot10\)
\(=\frac{70}{10}=7\)
chúc bạn hok tốt!