1)

( y - 1/5 ) : 2/3 = 3/4

y - 1/5            = 3/4 x 2/3

y - 1/5            = 1/2

y                   = 1/2 + 1/5

y                   = 7/10.

2)

7/4 - y x 5/6 = 1/2 + 1/3

7/4 - y x 5/6 = 5/6

7/4 - y         = 5/6 : 5/6

7/4 - y         = 1

y                = 7/4 - 1

y                = 3/4

C1 :(y-1/5):2/3=3/4

y-1/5=3/4.2/3

y-15=1/2

y=1/2+15

y=31/2

C2:

7/4-y.5/6=1/2+1/3

7/4-y.5/6=5/6

y.5/6=7/4-5/6

y.5/6=11/12

y=11/12:5/6

y=11/10

Cho mk sửa lại

C1 :(y-1/5):2/3=3/4

y-1/5=3/4.2/3

y-15=1/2

y=1/5+15

y=7/10

C2:

7/4-y.5/6=1/2+1/3

7/4-y.5/6=5/6

y.5/6=7/4-5/6

y.5/6=11/12

y=11/12:5/6

y=11/10

a, y=9/10

b,y=25/14

a ) y = 9/10

b ) y = 25/14

a) y=9/10

b)y =25/14

y = 0,125

=>2,5y=5,55

hay y=2,22

Đáp án B

\(1,25\times y=2,4+7,6\)

\(1,25\times y=10\)

                \(y=10:1,25\)

                \(y=8\)

\(\text{1,25 x y = 2,4 + 7,6}\)

\(\Rightarrow\text{1,25 x y = }\text{10}\)

\(\Rightarrow\text{ y = 10}:1,25=\text{8}\)

\(\text{Vậy y = 8}\)

1,25 x y = 2,4 + 7,6. Vậy 1,25 x y =10

           y = 10 : 1,25

           y = 8

Để A=12, ta có:

\(\dfrac{\left(y+4,25\right):0,5}{\left(5,25-4,75\right)\times2,5}=12\\ \dfrac{\left(y+4,25\right):0,5}{0,5\times2,5}=12\\ \dfrac{\left(y+4,25\right)\times2}{1,25}=12\\ y+4,25=12\times1,25:2=7,5\\ y=7,5-4,25=3,25\)

a, Thay y=5 vào A:

\(A=\dfrac{\left(y+4,25\right):0,5}{\left(5,25-4,75\right)\times2,5}=\dfrac{\left(5+4,25\right)\times2}{0,5\times2,5}=\dfrac{9,25\times2}{1,25}=\dfrac{19}{1,25}=15,2\)