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a) y × 2/5 + y × 3/5 = 5/7
y x ( 2/5 + 3/5) = 5/7
y x 5/5 = 5/7
y x 1 = 5/7
y = 5/7 : 1
y = 5/7
b) y × 7/2 - y × 3/2 = 3/4
y x ( 7/2 - 3/2) = 3/4
y x 4/2 = 3/4
y x 2 = 3/4
y = 3/4 : 2
y = 3/4 x 1/2
y = 3/8
`a,yxx(2/5+3/5)=5/7`
`y xx1=5/7`
`y=5/7:1`
`y=5/7`
`b,y xx(7/2-3/2)=3/4`
`y xx2=3/4`
`y =3/4:2`
`y=3/2`
![](https://rs.olm.vn/images/avt/0.png?1311)
y x 2/5 =8/21
y= 8/21:2/5
y= 20/21
12/7: y =7/5-2/5
12/7:y = 1
y = 12/7 :1
y= 12/7
\(y\times\dfrac{2}{5}=\dfrac{8}{21}\\ y=\dfrac{8}{21}:\dfrac{2}{5}\\ y=\dfrac{20}{21}\\ \dfrac{12}{7}:y+\dfrac{2}{5}=\dfrac{7}{5}\\ \dfrac{12}{7}:y=\dfrac{7}{5}-\dfrac{2}{5}\\ \dfrac{12}{7}:y=1\\ y=\dfrac{12}{7}:1=\dfrac{12}{7}\)
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\(1)\frac{12}{7}\times \frac{7}{4}+\frac{35}{11}:\frac{245}{121}\)
\(=3+\frac{35}{11}\times \frac{121}{245}\)
\(=3+\frac{11}{7}\)
\(= 3\frac{1}{7}(=\frac{22}{7})\)
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Bài 1:
a,Ta có:\(\frac{3}{5}=\frac{3\times2}{5\times2}=\frac{6}{10}\) (1)
\(\frac{4}{5}=\frac{4\times2}{5\times2}=\frac{8}{10}\) (2)
Từ (1) và (2)=> Một phân số tối giản nằm giữa hai phân số trên là:\(\frac{7}{10}\)
b,Ta có:\(\frac{3}{5}=\frac{3\times3}{5\times3}=\frac{9}{15}\)
\(\frac{4}{5}=\frac{4\times3}{5\times3}=\frac{12}{15}\)
=> hai phân số ở giữa là:\(\frac{10}{15}=\frac{2}{3};\frac{11}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a/ (y+2/9):7/4=11/7
y+2/9=11/7.7/4
y+2/9=11/4
y=11/4-2/9
y=91/36
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\(\frac{4}{x}\)=\(\frac{2}{7}\)
=>x=\(\frac{4x7}{2}\)
<=>x=14
\(\frac{y}{21}\)=\(\frac{2}{7}\)
=>y=\(\frac{21x2}{7}\)
<=>y=6
Vậy ...........
k cho mk nha
![](https://rs.olm.vn/images/avt/0.png?1311)
`7/2 : y= 3/8 + 5/4`
`=> 7/2 : y= 3/8 +10/8`
`=> 7/2 : y=13/8`
`=> y= 7/2 : 13/8`
`=> y= 7/2 xx 8/13`
`=> y= 28/13`
`4/7 - y xx 2=2/7`
`=> y xx 2= 4/7-2/7`
`=> y xx 2=2/7`
`=>y=2/7 : 2`
`=>y=2/7xx1/2`
`=>y=2/14`
`=>y=1/7`
4/7 - y x 2 = 2/7
y x 2 = 4/7 - 2/7
y x 2 = 2/7
y = 2/7 : 2 = 1/7