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Câu b
Ta có :x + 3 /1.3 +3/3.5 + 3/5.7+...+3/13.15=2 1/5
X + 2/3.(1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)1=11/5
X+2/3.(1-1/15)=11/5
X+ 2/3.14/15=11/5
X + 28/45=11/5
X = 11/5 -28/45
X=71/45
Câu a gợi ý
1/2-1/3/1/6=0
1/2- 1/3 - 1/6 ) x (1/2 + 2/3 + 3/4 +4/5 + .......+ 2019 /2020 ) =0
3/4:x=9/10
X = 3/4:9/10
X = 5/6
Bai 1 :
27 x 36 + 27 x 45 - 27
= 27 x 36 + 27 x 45 - 27 x 1
= 27 x ( 36 + 45 - 1 )
= 27 x 80
= 21260
Bai 2 :
a) 720 : [ 41 - ( 2 . x - 5 ) ] = 120
41 - ( 2 . x - 5 ) = 720 : 120
41 - ( 2 . x - 5 ) = 6
2 . x - 5 = 41 - 6
2 . x - 5 = 35
2 . x = 35 + 5
2 . x = 40
x = 40 : 2
x = 20
b) ( 3,7 : x - 13 ) x 0,2 - 1,4 = 10,8
( 3,7 : x - 13 ) x 0,2 = 10,8 + 1,4
( 3,7 : x - 13 ) x 0,2 = 12,2
3,7 : x - 13 = 12,2 : 0,2
3,7 : x - 13 = 61
3,7 : x = 61 + 13
3,7 : x = 74
x = 74 : 3,7
x = 20
a.27x36+27x45-27
=27x(36+45-1)
=27x80
=2160
a. 720:[41-(2*x-5)]=120
41-(2*x-5)=720:120=6
2*x-5=41-6=35
2*x=35+5=40
x=40:2=20
Vậy x=20
b. (3,7:x-13)x0,2-1,4=10,8
(3,7:x-13)x0,2=10,8+1,4=11,2
3,7:x-13=11,2:0,2=56
3,7:x=56+13=69
x=3,7:69=\(\frac{37}{690}\)
27*18*15=7290
3.8*2.5*4=38
1.9*1.4*1.5=3.99
\(\frac{4}{3}x\frac{5}{4}x\frac{2}{3}=\frac{10}{9}\)
15.5*6.4*10=992
1.75*0.4*0.8=0.56
8*5*4.5=180
2*0.5*0.75=0.75
(15-12)*10.5*8=252
10*4.5*12=540
= 7290
= 38
= 3,99
= 10 / 9
= 992
= 0,56
= 180
= 0,75
= 252
= 540
Bài 2:
\(B=\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right).......\left(1-\frac{1}{2004}\right)\)
\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}....\frac{2003}{2004}\)
\(=\frac{1}{2004}\)
\(x(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{132}=\) \(5\frac{1}{2}\)
\(x\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{11\cdot12}\right)=\frac{11}{2}\)
\(x\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{11}-\frac{1}{12}\right)=\frac{11}{2}\)
\(x\left(1-\frac{1}{12}\right)=\frac{11}{2}\)
\(x\cdot\frac{11}{12}=\frac{11}{2}\)
\(x=\frac{11}{2}:\frac{11}{12}\)
\(x=6\)
Vậy x = 6
\(\frac{x}{2}+\frac{x}{6}+\frac{x}{12}+\frac{x}{20}+...+\frac{x}{132}=5\frac{1}{2}\)
\(\Rightarrow x\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\right)=\frac{11}{2}\)
\(\Rightarrow x\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{11.12}\right)=\frac{11}{2}\)
\(\Rightarrow x\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}=\frac{11}{2}\right)\)
\(\Rightarrow x\left(1-\frac{1}{12}\right)=\frac{11}{2}\)
\(\Rightarrow x.\frac{11}{12}=\frac{11}{12}\)
\(\Rightarrow x=\frac{11}{12}:\frac{11}{12}=1\)
Vậy x = 1
1.
a ) x * 3.1 + x * 1,4 = 2,7
x * ( 3,1 + 1,4 ) = 27
x * 4,5 = 27
x = 27 : 4,5=6
Vậy x=6
b) x : 3,08 -17,8 = 158 , 2
x : 3, 08 = 158,2 + 17,8
x : 3, 08 = 176
x = 176 * 3,08
x = 542,08
Vậy x= 542,08
\(1\frac{2}{5}\)tấn = 1400 kg
1) \(x\times3,1+x\times1,4=27\)
=> \(x\times\left(3,1+1,4\right)=27\)
=> \(x\times4,5=27\)
=> \(x=27:4,5\)
=> \(x=6\)