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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)
a) y + 3/7 x 21/9 = 5
y + 3/7 x 7/3 = 5
y + 1 = 5
y = 4
b) y x 3/5 - 1/2 = 4/5
y x 3/5 = 4/5 + 1/2
y x 3/5 = 13/10
y = 13/6
c) 9/8 - y + 2/5 = 1/4
y - 2/5 = 9 /8 - 1/4
y - 2/5 = 7/8
y = 51/40
d) y - 6/5 : 2/3 = 5/6
y - 9/5 = 5/6
y = 79/30
e) y : 7/8 + 3/4 = 7/4
y : 7/8 = 1
y = 7/8
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a) y = 5/14 : 6/7
y = 5/12
vậy y = 5/12
b) y = 4/9 x 2/3
y = 8/27
vậy t = 8/27
c) y = 1/2 - 3/10
y = 1/5
vậy y = 1/5
d) y = 5/6 - 1/3
y = 1/2
vậy y = 1/2
![](https://rs.olm.vn/images/avt/0.png?1311)
\(12:y=\frac{3}{4}+\frac{4}{5}\)
\(12:y=\frac{15}{20}+\frac{16}{20}\)
\(12:y=\frac{31}{20}\)
\(y=12:\frac{31}{20}\)
\(y=12x\frac{20}{31}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}xY=1\)
\(y=1:\frac{4}{5}\)
\(y=1x\frac{5}{4}\)
\(y=\frac{5}{4}\)
\(\frac{37}{63}-y=\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{1}{7}\)
\(y=\frac{37}{63}-\frac{9}{63}\)
\(y=\frac{28}{63}\)
\(y=\frac{4}{9}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y:\frac{3}{7}=\frac{3}{42}+\frac{30}{42}\)
\(y:\frac{3}{7}=\frac{33}{42}\)
\(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{11}{14}x\frac{3}{7}\)
\(y=\frac{33}{98}\)
\(12:y=\frac{3}{4}+\frac{4}{5}\) \(\frac{37}{63}-y=\frac{1}{7}\)
\(12:y=\frac{31}{20}\) \(y=\frac{37}{63}-\frac{1}{7}\)
\(y=12:\frac{31}{20}\) \(y=\frac{4}{9}\)
\(y=\frac{240}{31}\)
\(\frac{4}{5}\cdot y=1\) \(y:\frac{3}{7}=\frac{3}{42}+\frac{5}{7}\)
\(y=1:\frac{4}{5}\) \(y:\frac{3}{7}=\frac{11}{14}\)
\(y=\frac{5}{4}\) \(y=\frac{11}{14}.\frac{3}{7}\)
\(y=\frac{33}{98}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
`x<3`
`->x= 1;2`
`----`
`1/5 < y/5<1`
`->1/5 < y/5<5/5`
`->y=2;3;4`
`-----`
`4/x=y/21=2/7`
\(\rightarrow\left\{{}\begin{matrix}\dfrac{4}{x}=\dfrac{y}{21}\\\dfrac{y}{21}=\dfrac{2}{7}\end{matrix}\right.\rightarrow\left\{{}\begin{matrix}\dfrac{4}{14}=\dfrac{6}{21}\\\dfrac{6}{21}=\dfrac{2}{7}\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{1}{5}+y=7\)
\(y=7-\dfrac{1}{5}\)
\(y=\dfrac{35}{5}-\dfrac{1}{5}\)
\(y=\dfrac{34}{5}\)
_________________________
\(y:\dfrac{3}{4}=\dfrac{5}{7}\)
\(y=\dfrac{5}{7}\times\dfrac{3}{4}\)
\(y=\dfrac{15}{28}\)
Chúc bạn học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
bài 1 :
\(\frac{5}{12}\) + \(\frac{1}{3}\) = \(\frac{5}{12}\) + \(\frac{4}{12}\) = \(\frac{5+4}{12}\) = \(\frac{9}{12}\) = \(\frac{3}{4}\)
1 - \(\frac{3}{4}\) = \(\frac{4}{4}\) - \(\frac{3}{4}\) = \(\frac{4-3}{4}\) = \(\frac{1}{4}\)
2 x \(\frac{3}{11}\) = \(\frac{2x3}{11}\) = \(\frac{6}{11}\)
\(\frac{8}{7}\): 4 = \(\frac{8}{7x4}\) = \(\frac{8}{28}\) = \(\frac{2}{7}\)
bài 2 :
\(\frac{2}{5}\) : y = \(\frac{1}{3}\)
y = \(\frac{2}{5}\) : \(\frac{1}{3}\)
y = \(\frac{6}{5}\)
y : \(\frac{7}{11}\) = 22
y = 22 x \(\frac{7}{11}\)
y = 14
ai thấy đúng tk nha
![](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
\(y\times\dfrac{2}{5}=\dfrac{8}{21}\\ y=\dfrac{8}{21}:\dfrac{2}{5}\\ y=\dfrac{20}{21}\\ \dfrac{12}{7}:y+\dfrac{2}{5}=\dfrac{7}{5}\\ \dfrac{12}{7}:y=\dfrac{7}{5}-\dfrac{2}{5}\\ \dfrac{12}{7}:y=1\\ y=\dfrac{12}{7}:1=\dfrac{12}{7}\)
y : \(\dfrac{1}{5}\) = 7
y = 7 \(\times\) \(\dfrac{1}{5}\)
y = \(\dfrac{7}{5}\)
\(\dfrac{5}{4}\) - y = \(\dfrac{2}{3}\)
y = \(\dfrac{5}{4}\) - \(\dfrac{2}{3}\)
y = \(\dfrac{7}{12}\)
\(y:\dfrac{1}{5}=7\)
\(y=7\times\dfrac{1}{5}\)
\(y=\dfrac{7}{5}\)
_____________________
\(\dfrac{5}{4}-y=\dfrac{2}{3}\)
\(y=\dfrac{5}{4}-\dfrac{2}{3}\)
\(y=\dfrac{15}{12}-\dfrac{8}{12}\)
\(y=\dfrac{7}{12}\)
Chúc bạn học tốt