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![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1: Tính nhanh
A, 13 x 126 + 37 x 126 - 49 x 126
= 126 x ( 13 + 49 - 49 )
= 126 x 1
= 126
B, ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x 102 - 101 x 101 - 50 - 51 )
= ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x ( 102 - 101 - 1))
= ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x 0)
= ( 1 + 2 + 4 + 8+.....+ 512 ) x 0
= 0
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(x+\dfrac{4}{9}=\dfrac{5}{27}\)
\(x=\dfrac{5}{27}-\dfrac{4}{9}\)
\(x=-\dfrac{7}{27}\)
b) \(x-\dfrac{4}{11}=\dfrac{7}{33}\)
\(x=\dfrac{7}{33}+\dfrac{4}{11}\)
\(x=\dfrac{19}{33}\)
c) \(\dfrac{8}{5}-x=\dfrac{1}{3}\times\dfrac{2}{5}\)
\(\dfrac{8}{5}-x=\dfrac{2}{15}\)
\(x=\dfrac{8}{5}-\dfrac{2}{15}\)
\(x=\dfrac{22}{15}\)
d) \(x-\dfrac{3}{4}=\dfrac{1}{2}+\dfrac{2}{6}\)
\(x-\dfrac{3}{4}=\dfrac{5}{6}\)
\(x=\dfrac{5}{6}+\dfrac{3}{4}\)
\(z=\dfrac{19}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\left(1+2+4+...+408\right)\cdot\left[101\left(102-101-1\right)\right]=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
54 x 275 + 825 x 15 + 275
=14850 + 825 x 15 + 275
=14850 + 12375+275
=14850 + 12650
=27500
477x1998-1998x427
=1998x(477-427)
=1998x50
=99900
1985:2+15:2
=(1985+15):2
=2000:2
=1000
40x113x25-20x112x50
=(40x25)x113-(20x50)x112
=1000x113-1000-112
=1000x(113-112)
=1000x1
=1000
câu 1, ??????????????
câu 2, [477-427], +[1998-1998]=50+0=50
câu 3,[1985+15]:2=2000:2=1000
câu 4, ??????????
chú thích ? là ko có cách tính nhanh
![](https://rs.olm.vn/images/avt/0.png?1311)
a,Cách 1: (6/11 + 5/11 ) x 3/7 Cách 2 :(6/11 + 5/11) x 3/7
= 1 x 3/7 =6/11 x 3/7 + 5/11 x 3/7
= 3/7 = 18/77 + 15/77
= 3/7
b, Cách 1:3/5 x 7/9 - 3/5 x 2/9 Cách 2 :3/5 x 7/9 - 3/5 x 2/9
= 7/15 - 2/15 = 3/5 x (7/9 - 2/9 )
= 1/3 = 3/5 x 5/9
= 1/3
c, Cách 1:(6/7 - 4/7) : 2/5 Cách 2: ( 6/7- 4/7 ) : 2/5
= 2/7 : 2/5 = 6/7 : 2/5 - 4/7 : 2/5
= 5/7 = 15/7 - 10/7
= 5/7
d,Cách 1:8/15 : 2/11 + 7/15 : 2/11 Cách 2:8/15 : 2/11 +7/15 : 2/11
= 88/30 + 77/30 =(8/15+7/15) :2/11
= 11/2 = 1 : 2/11
= 11/2
Bài 2 cậu tự làm nhé !
a/ (x+1)+(x+2)+(x+3)+....+(x+50)=2275
<=> (x+x+...+x)+(1+2+3+...+50)=2275
<=> \(50x+\frac{50\left(50+1\right)}{2}=2275\)
<=> 50.x+1275=2275
<=> 50x=1000
=> x=1000:50 => x=20
b/ x04+40x=101x11
<=> 100x+4+400+x=1111
<=> 101x=707
=> x=707:101 => x=7
a, ( x + 1 ) + ( x + 2 ) + ( x + 3 ) + ... + ( x + 50 ) = 2275
x x 50 + ( 50 + 1 ) x ( 50 : 2 ) = 2257
x x 50 + 51 x 25 = 2257
x x 50 + 1275 = 2257
x x 50 = 2257 - 1275
x x 50 = 982
x = 982 : 50
x = 19,64