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246 x 2005 - 2005 x 148 = 2005 x ( 246 - 148 )
= 2005 x 98
= 196490
![](https://rs.olm.vn/images/avt/0.png?1311)
a)23+23*2+23*3+23*4
=23*(1+2+3+4)
=23*10
=230
b)246*2005-2005*148+2005*2
=(246-148+2)*2005
=100*2005
=200500
c)25*12*30*4
=(25*4)*(12*30)
=100*360
=36000
Câu d làm tương tự câu b
![](https://rs.olm.vn/images/avt/0.png?1311)
246 x2005-2005x148+2005x102
=2005 x (246-148+102)
=2005 x 200
=401 000
HT
![](https://rs.olm.vn/images/avt/0.png?1311)
1/
25x12x30x4
= (25x4)x(12x30)
=100x3600
=360 000
2/
23+23x2+23x3+23x4
=23x1+23x2+23x3+23x4
=23x(1+2+3+4)
=23x10
=230
3/
248x2005 - 2005x148
=(248-148)x2005
=100x2005
=200500
1/
25x12x30x4
= (25x4)x(12x30)
=100x3600
=360 000
2/
23+23x2+23x3+23x4
=23x1+23x2+23x3+23x4
=23x(1+2+3+4)
=23x10
=230
3/
248x2005 - 2005x148
=(248-148)x2005
=100x2005
=200500
![](https://rs.olm.vn/images/avt/0.png?1311)
=2008x1+2008x1+2008x1+2008x1-2008x4
=2008x(1+1+1+1-4
=2008x0
=0
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45 x 22 + 45 x 18
= 45 x ( 18+ 22)
= 45 x 40
= 1000
![](https://rs.olm.vn/images/avt/0.png?1311)
Đặt :
\(A=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\)
\(\Rightarrow2A=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\)
\(\Rightarrow2A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\)
\(\Rightarrow2A=\frac{1}{3}-\frac{1}{11}\)
\(\Rightarrow2A=\frac{3}{11}\)
\(\Rightarrow A=\frac{3}{22}\)
246x2005-2005x148
=2005x(246-148)
=2005x98
=196490
246x2005-2005x148
= (246-148)x2005
=98x2005
=196490