\(a,y-\dfrac{3}{4}=\dfrac{5}{12}:\dfrac{10}{3}\\ \Rightarrow a,y-\dfrac{3}{4}=\dfrac{5}{12}.\dfrac{3}{10}\\ \Rightarrow y-\dfrac{3}{4}=\dfrac{1}{8}\\ \Rightarrow y=\dfrac{1}{8}+\dfrac{3}{4}\\ \Rightarrow y=\dfrac{7}{8}\\ b,\dfrac{1}{3}\times\left(\dfrac{2}{5}+\dfrac{3}{10}\right):\dfrac{14}{9}=\dfrac{1}{3}\times\left(\dfrac{4}{10}+\dfrac{3}{10}\right):\dfrac{14}{9}=\dfrac{1}{3}\times\dfrac{7}{10}\times\dfrac{9}{14}=\dfrac{3}{20}\)

x có thể là: 1,4,7,2,5,8

y có thể là: 0,5

Hok tốt

Đề đúng phải như này 

\(\dfrac{3}{7}\) <  y <  \(\dfrac{4}{7}\) 

\(\dfrac{3}{7}\) = \(\dfrac{3\times5}{7\times5}\) = \(\dfrac{15}{35}\)                                       \(\dfrac{4}{7}\) = \(\dfrac{4\times5}{7\times5}\) = \(\dfrac{20}{35}\)

Bốn phân số thỏa mãn đề bài lần lượt là:

\(\dfrac{16}{35}\); \(\dfrac{17}{35}\); \(\dfrac{18}{35}\); \(\dfrac{19}{35}\)

\(\dfrac{3}{7}=\dfrac{30}{70};\dfrac{4}{7}=\dfrac{40}{70}\)

=> 4 giá trị thỏa mãn là: \(\dfrac{31}{70};\dfrac{33}{70};\dfrac{37}{70};\dfrac{39}{70}\)

Vì y x4 < 1 => y x 4 = 0. => y =0.

b, Vì 7 x y < 20 

=> 7 x y = 7 hoặc 7 x y = 14.

=> y =1 hoặc y =2.

\(\frac{2}{3}x\frac{4}{y}=\frac{4}{45}:\frac{1}{5}\)\(=\frac{4}{15}\)

\(\frac{4}{y}=\frac{4}{15}:\frac{2}{3}\)\(=\frac{2}{5}\)

y=4:\(\frac{2}{5}\)    y=10

\(\frac{3}{4}x\frac{y}{5}=\frac{15}{4}\)

\(\frac{y}{5}=\frac{15}{4}:\frac{3}{4}=5\)

y=5x5=25

60

y x 2 + y x 3 + y x 5 = 9600

y x ( 2 + 3 + 5 ) = 9600

y x 10 = 9600

y = 9600 : 10

y = 960

_HT_

Y=5/6

Thay y = 123 vào A = y + y x 2 + y x 3 + y x 4 - 456, ta có:

A = 123 + 123 x 2 + 123 x 3 + 123 x 4 - 456

A = 123 x (1 + 2 + 3 + 4) - 456

A = 123 x 10 - 456

A = 1230 - 456

A = 774