a.\(y:\dfrac{4}{5}=\dfrac{11}{8}\)

\(y=\dfrac{11}{8}\times\dfrac{4}{5}\)

\(y=\dfrac{11}{10}\)

b.\(\dfrac{11}{3}-y=\dfrac{1}{9}\)

\(y=\dfrac{11}{3}-\dfrac{1}{9}\)

\(y=\dfrac{32}{9}\)

c.\(\dfrac{1}{7}\times x=\dfrac{8}{5}\)

\(x=\dfrac{8}{5}:\dfrac{1}{7}\)

\(x=\dfrac{56}{5}\)

\(y=\dfrac{11}{8}.\dfrac{4}{5}\)

\(y=\dfrac{44}{40}\)

\(x=\dfrac{11}{3}-\dfrac{1}{9}\)

\(x=\dfrac{99-3}{27}=\dfrac{96}{27}\)

\(x=\dfrac{8}{5}:\dfrac{1}{7}\)

\(x=\dfrac{56}{5}\)

a)\(y=\dfrac{4}{5}\times\dfrac{11}{8}=\dfrac{44}{40}=1\dfrac{4}{40}\)

b)\(y=\dfrac{11}{3}-\dfrac{1}{9}=\dfrac{33}{9}-\dfrac{1}{9}=\dfrac{32}{9}\)

c)\(x=\dfrac{8}{5}\times7=\dfrac{56}{5}\)

24/y=3/5*8/3

24/y=8/5

24:y=8/5

y=24;8/5

y=15

b,42/25:y/5=6/7

y/5=42/25:6/7

y/5=49/25

y:5=49/25

y=49/25*5

y=49/5=9,8

\(\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)

\(\Rightarrow\frac{24}{y}=\frac{3}{5}\times\frac{8}{3}\)

\(\Rightarrow\frac{24}{y}=\frac{8}{5}\)

\(\Rightarrow y=\frac{8}{5}\times24=\frac{192}{5}\)

b , \(\frac{42}{25}:\frac{y}{5}=\frac{6}{7}\)

\(\Rightarrow\frac{y}{5}=\frac{6}{7}\times\frac{42}{25}=\frac{36}{25}\)

\(\Rightarrow y=\frac{36}{25}\times5=\frac{36}{5}\)

\(\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)                \(\frac{42}{25}:\frac{y}{5}=\frac{6}{7}\)

\(\frac{24}{y}=\frac{3}{5}\cdot\frac{8}{3}\)                      \(\frac{y}{5}=\frac{42}{25}:\frac{6}{7}\)

\(\frac{24}{y}=\frac{8}{5}\)                                \(\frac{y}{5}=\frac{42}{25}\cdot\frac{7}{6}\)

\(\Rightarrow8y=24\cdot5\)                         \(\frac{y}{5}=\frac{49}{25}\)

\(8y=120\)                                 \(\Rightarrow25y=5\cdot49\)

\(y=15\)                                            \(25y=245\)

                                                                \(y=\frac{49}{5}\) 

jhbmjbnhm b

\(a,\frac{42}{25}:\frac{y}{5}=\frac{6}{5}\)

\(\frac{y}{5}=\frac{42}{25}:\frac{6}{5}\)

\(\frac{y}{5}=\frac{42}{25}\times\frac{5}{6}\)

\(\frac{y}{5}=\frac{7}{5}\)

\(\Leftrightarrow5y=7.5\)

\(5y=35\)

\(y=7\)

\(b,\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)

\(\frac{24}{y}=\frac{3}{5}\times\frac{8}{3}\)

\(\frac{24}{y}=\frac{8}{5}\)

\(\Leftrightarrow8y=24.5\)

\(8y=120\)

\(y=15\)

\(\frac{5}{6}y=\frac{3}{2}\)

\(y=\frac{3}{2}:\frac{5}{6}\)

\(y=\frac{3}{2}\times\frac{6}{5}\)

\(y=\frac{9}{5}\)

Bài 1: 

Ta có:

\(y-x=25\Rightarrow y=25+x\)

Mà \(7x=4y\Rightarrow7x=4\cdot\left(25+x\right)\)

\(7x=100+4x\)

\(\Rightarrow7x-4x=100\)

\(3x=100\)

\(x=\frac{100}{3}\)

bài 1 :

Ta có: 7x=4y ⇔ x/4=y/7

áp dụng tính chất dãy tỉ số bằng nhau ta có 

x/4=y/7=(y-x)/(7-4)=100/3

⇒x= 4 x 100/3=400/3 ; y = 7 x 100/3=700/3

bài 2 

ta có x/5 = y/6 ⇔ x/20=y/24

         y/8 = z/7 ⇔ y/24=z/21

⇒x/20=y/24=z/21

ADTCDTSBN(bài 1 có)

x/20=y/24=z/21=(x+y)/(20+24)=69/48=23/16

⇒x= 20 x 23/16 = 115/4

   y= 24x 23/16=138/2

   z=21x23/16=483/16

bài 3

x:y:z=3:8:5  ⇔ x/3=y/8=z/5

ADTCDTSBN

x/3=y/8=z/5=(3x+y-4z)/(9+8-10)=14/7=2

⇒x = 2x3 = 6 ; y= 2x8=`16; z=2x5=10

5.7.77-7.60+49.25-15.42

= 5.7.77-7.5.12+7.7.5.5-3.5-3.5.6.7

= 35.77-35.12+35.35-35.18

= 35.(77-12+35-18)

= 35.82

= 2870

A.y/5 x 3/7 x 3 = 27/35.

   y/5 x 3/7      = 27/35 :3

  y/5 x 3/7        = 9/35

  y/5                = 9/35 :3/7

 y /5                = 3/5

y ;5                 = 3:5

y:5                  = 0,6

         y =         0,6 x5

      y = 3

A. y/5 x 3/7 x 3 = 27/35

     y/5 x 9/7      = 27/35

     y/5               = 3/5

       y                = 3

B.42/25 : y/5 = 1 : 5/6

   42/25 : y/5 = 6/5

              y/5  = 42/25 : 6/5

              y/5  = 7/5

               y    = 7