x = 20.m ; y = 20.n ; ƯCLN (m,n) = 1 ; m,n thuộc N*

20.m.20.n = 420

m,n = 420 : 400 => m,n không có giá trị thỏa mãn       

=> Vậy x,y không có giá trị thỏa mãn.
. k cho tớ hay không là tùy cậu TvT                 

. Á !! Tớ lộn rồi nha. Đừng ghi 

c)\(\dfrac{3}{8}\times\dfrac{5}{8}+y=\dfrac{5}{4}\) 

   \(\dfrac{15}{64}+y=\dfrac{5}{4}\) 

           \(y=\dfrac{5}{4}-\dfrac{15}{64}\) 

           \(y=\dfrac{65}{64}\)

d, \(\dfrac{3}{8}+\dfrac{5}{8}\times y=\dfrac{5}{4}\) 

          \(\dfrac{5}{8}\times y=\dfrac{5}{4}-\dfrac{3}{8}\) 

          \(\dfrac{5}{8}\times y=\dfrac{7}{8}\) 

                 \(y=\dfrac{7}{8}:\dfrac{5}{8}\) 

                \(y=\dfrac{7}{5}\)

 a, 3/4 x y = 3/5 + 3/10   

3/4 x y = 9/10

y = 9/10 : 3/4

y = 6/5

b, 3/5 : y = 3/4 - 2/5

3/5 : y = 7/20

y = 3/5 : 7/20 

y = 12/7

Bài 1:

Tổng của 2 số là

  \(36\times2=72\) 

Số lớn là

  \(72-17=55\) 

Bài 2:

a) \(4567+y\div34=10987\) 

                 \(y\div34=10987-4567\) 

                 \(y\div34=6420\) 

                         \(y=6420\times34\) 

                         \(y=218280\) 

b) \(\dfrac{4}{3}+\dfrac{1}{2}\div y=2\) 

             \(\dfrac{1}{2}\div y=2-\dfrac{4}{3}\) 

              \(\dfrac{1}{2}\div y=\dfrac{2}{3}\) 

                      \(y=\dfrac{1}{2}\div\dfrac{2}{3}\) 

                      \(y=\dfrac{3}{4}\) 

Bài 3:

a) \(\dfrac{2}{5}\times\dfrac{2}{5}+\dfrac{9}{8}\div3=\dfrac{4}{25}+\dfrac{9}{8}\times\dfrac{1}{3}=\dfrac{4}{25}+\dfrac{3}{8}=\dfrac{107}{200}\) 

b) \(2-\left(\dfrac{1}{7}\times4+\dfrac{5}{21}\right)=2-\left(\dfrac{4}{7}+\dfrac{5}{21}\right)=2-\dfrac{17}{21}=\dfrac{25}{21}\)

Bài 1 : Gọi a là số lớn, b là số bé, theo đề bài ta có :

(a+b):2=36⇒a+b=72

mà b=17

Nên a=72-17=55

Bài 2 :

a) 4567+y:34=10987

⇒ y:34=10987-4567

⇒ y:34=6420

⇒ y=6420x34

⇒ y=218280

b) \(\dfrac{4}{3}+\dfrac{1}{2}:y=2\)

\(\Rightarrow\dfrac{1}{2}:y=2-\dfrac{4}{3}\)

\(\Rightarrow\dfrac{1}{2}:y=\dfrac{2}{3}\)

\(\Rightarrow y=\dfrac{1}{2}:\dfrac{2}{3}\)

\(\Rightarrow y=\dfrac{1}{2}x\dfrac{3}{2}\)

\(\Rightarrow y=\dfrac{3}{4}\)

Bài 3 :

\(\dfrac{2}{5}x\dfrac{2}{5}+\dfrac{9}{8}:3=\dfrac{4}{25}+\dfrac{9}{8}x\dfrac{1}{3}=\dfrac{4}{25}+\dfrac{3}{8}\)

= \(\dfrac{4x8}{25x8}+\dfrac{25x3}{25x8}=\dfrac{32}{200}+\dfrac{75}{200}=\dfrac{107}{200}\)

\(2-\left(\dfrac{1}{7}x4+\dfrac{5}{21}\right)=2-\left(\dfrac{4}{7}+\dfrac{5}{21}\right)=2-\left(\dfrac{12}{21}+\dfrac{5}{21}\right)=2-\dfrac{17}{21}=\dfrac{42}{21}-\dfrac{17}{21}=\dfrac{25}{21}\)

1/2-2y=9/20

=>2y=1/2-9/20=1/20

=>y=1/20:2=1/40

b,3/5:4/3:y=2+7/10=9/20:y=27/10

=>y=9/20:27/10=1/6

c,y+y*3/2-y*1/2=1/10

=>y(1+3/2-1/2)=1/10

=>2y=1/10

=>y=1/10:2=1/20

a) \(980+y:94=8245\)

\(y:94=7265\)

\(y=7265\times94\)

\(y=682910\)

b) \(45\times y\times36=3240\)

\(45\times y=3240:36\)

\(45\times y=90\)

\(y=90:45\)

\(y=2\)

c) \(3865-y+875=1000\)

\(3865-y=125\)

\(y=3865-125\)

\(y=3740\)

d) \(4788:126\times y=1596\)

\(126\times y=4788:1596\)

\(126\times y=3\)

\(y=\dfrac{3}{126}\)

\(y=\dfrac{1}{42}\)

e) \(24624:y:9=76\)

\(y:9=24624:76\)

\(y:9=324\)

\(y=324\times9\)

\(y=2916\)

A) x/y-3/8=1                  x/y-3/8=1/2                          B)4/9:x/y=1                                                    4/9:x/y=2/3 

x/y=1+3/8                     x/y=1/2+3/8                                   x/y=4/9:1                                                    x/y=4/9:2/3

x/y=8/8+3/8                  x/y=4/8+3/8                                   x/y=4/9                                                       x/y=2/3

x/y=11/8                       x/y=7/8

a   x/y=1 và 1/2+3/8

x/y=15/8

b   x/y=4/9:1 và 2/3

x/y=4/15

Ta có : \(\frac{x}{4}=\frac{y}{7}\) 

\(\Rightarrow\frac{x^2}{16}=\frac{y^2}{49}=\frac{3x^2}{48}=\frac{4y^2}{196}=\frac{3x^2-4y^2}{48-196}=\frac{100}{-148}=-\frac{25}{37}\)

Thay vào là ra nhé !:D

Cái chỗ Nguyễn Quang Trung đúng ròi

\(\Rightarrow\hept{\begin{cases}\frac{x}{4}=-\frac{25}{37}\\\frac{y}{7}=-\frac{25}{37}\end{cases}}\Rightarrow\hept{\begin{cases}x=-\frac{100}{37}\\y=-\frac{175}{37}\end{cases}}\)

\(a,2\dfrac{2}{5}:y\times1\dfrac{3}{4}=\dfrac{7}{8}\\ \dfrac{12}{5}:y\times\dfrac{7}{4}=\dfrac{7}{8}\\ \dfrac{12}{5}:y=\dfrac{7}{8}:\dfrac{7}{4}\\ \dfrac{12}{5}:y=\dfrac{1}{2}\\ y=\dfrac{12}{5}:\dfrac{1}{2}=\dfrac{24}{5}\\ b,3\dfrac{2}{5}:y:1\dfrac{1}{4}=2\dfrac{3}{5}\\ \dfrac{17}{5}:y:\dfrac{5}{4}=\dfrac{13}{5}\\ y:\dfrac{5}{4}=\dfrac{17}{5}:\dfrac{13}{5}\\ y:\dfrac{5}{4}=\dfrac{17}{13}\\ y=\dfrac{17}{13}\times\dfrac{5}{4}=\dfrac{85}{52}\)

\(c,\dfrac{12}{5}-2\dfrac{2}{5}\times y=1\dfrac{1}{4}\\ \dfrac{12}{5}-\dfrac{12}{5}\times y=\dfrac{5}{4}\\ \dfrac{12}{5}\times y=\dfrac{12}{5}-\dfrac{5}{4}\\ \dfrac{12}{5}\times y=\dfrac{23}{20}\\ y=\dfrac{23}{20}:\dfrac{12}{5}\\ y=\dfrac{23}{48}\)

bài 1

a, X/Y x 1/5=3/10

X/Y=3/10:1/5

X/Y=3/2

b, 3/4 x X/Y= 6/5

X/Y=3/4:6/5

X/Y=5/8

Bài 2:

a, >     b, <       c,=        d,<