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a) \(20\times6\times5\times7\)
\(=\left(20\times5\right)\times6\times7\)
\(=100\times6\times7\)
\(=4200\)
b) \(16\times4\times5\times20\)
\(=16\times4\times100\)
\(=16\times400\)
\(=6400\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: 34/56=17/28=1-11/28
42/53=1-11/53
mà 11/28>11/53
nên 34/56<42/53
b: 5/4=15/12; 7/6=14/12; 5/6=10/12
=>5/4>7/6>5/6
c: 4/3>1>99/100
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\left(\dfrac{1}{6}+\dfrac{5}{6}\right)+\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{11}{16}+\dfrac{5}{16}\right)=1+1+1=3\)
\(=\left(\dfrac{1}{6}+\dfrac{5}{6}\right)+\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{11}{16}+\dfrac{5}{16}\right)\\ =1+1+1=3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
2/9+3/9+4/9+5/9+6/9+7/9
=2+3+4+5+6+7/9
=27/9
=3
1/6+4/9+5/6+11/16+5/9+5/16
=1/6+5/6+4/9+5/9+11/16+5/16
=1+1+1=3
hok tốt ~
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dấu . là nhân hay là phần ngăn cách ở hàng phần nghìn thế
![](https://rs.olm.vn/images/avt/0.png?1311)
b,21/17x13/14x56x3/42
=21/17x3/42x56x13/14
=21x3/17x42 x 56x13/14
=21x3/17x21x2 x 14x4x13/14
=3/17x2 x 4x13
=3/24 x 52=3x52/24
=3x52/3x8
=52/8=13/2
a, 6/7 x 16/15 x 7/6 x 21/32
=(6/7 x 7/6)x16/15x21/32
=16/15x21/32
=16x21/15x32
=16x3x7/3x5x16x2
=7/5x2=7/10
a)32:5+53:5
=(32+53):5
=85:5
=17
_______________________________________
b)100:6-16:6
=(100-16):6
=84:6
=14
a (53+32):5
=85:5
=17
b(100-16):6
=84:6
=14