Lời giải:
a.

$x=\frac{7}{25}+\frac{-1}{5}=\frac{7}{25}+\frac{-5}{25}=\frac{7-5}{25}=\frac{2}{25}$

b.

$x=\frac{5}{11}+\frac{4}{-9}=\frac{5}{11}-\frac{4}{9}=\frac{45}{99}-\frac{44}{99}=\frac{1}{99}$

c.

$\frac{x}{-1}=\frac{-1}{3}-\frac{5}{9}=\frac{-3}{9}-\frac{5}{9}=\frac{-8}{9}$

$x=(-1).\frac{-8}{9}=\frac{8}{9}$

1) x = 4/5 - 1/3

x = 7/15

2) 5/3.x=1/21

x=1/35

3) -12/13.x = 1/13

x=-1/12

7) th1: x-1=2/3

x = 5/3

Th2: x - 1 = -2/3

x=1/3

a: =>4/x=y/21=4/7

=>x=7; y=21*4/7=12

b: x/7=9/y

=>xy=63

mà x>y

nên \(\left(x,y\right)\in\left\{\left(63;1\right);\left(21;3\right);\left(9;7\right);\left(-7;-9\right);\left(-3;-21\right);\left(-1;-63\right)\right\}\)

c: x/15=3/y

=>xy=45

mà x<y<0

nên \(\left(x,y\right)\in\left\{\left(-45;-1\right);\left(-15;-3\right);\left(-9;-5\right)\right\}\)

d: x/y=21/28=3/4

=>x/3=y/4=k

=>x=3k; y=4k(k\(\in Z\))

` 1, 5 . ( -2/25 = 3/2 . (-2)/25 = -6/50 = -3/25 `

` 1 3/5 . (-3)/4 = 8/5 . (-3)/4 = -24/20 = -6/5 `

`-15/4 : 21/(-1) = -15/4 . (-1)/21 = 15/84 = 5/28 `

` ( -2 1/7 ) : ( -1 1/14 ) = (-15)/7 : (-15)/14 = -15/7 . (-14)/15 =  210/105 = 2 ` 

`@animephamdanhv.`

giúp với

1/ \(\frac{7.25-49}{7.24+21}=\frac{7.25-7\cdot7}{7\cdot24+7\cdot3}=\frac{7\left(25-7\right)}{7\left(24+3\right)}=\frac{25-7}{24+3}=\frac{18}{27}\)

2/Vậy số đó là: 1.5/2/5=3.75

bài 2 :

   Số cần tìm là :

         1,5 : \(\frac{2}{5}\)% = 1,5 : \(\frac{1}{250}\) = 375

 Hồi nãy mình nhầm !!!!

Bài 3: 15-(15-x)=-x-(25+9)

15-15+x=-x-25-9

x+x=-25-9-15+15

2x=-34

x=-34:2

x=-17

Bài 1: Dễ, tính máy tính là ra

Bài 2:

a) \(\dfrac{1}{5}+1\dfrac{1}{4}x=\dfrac{2}{3}\)

\(\Rightarrow1\dfrac{1}{4}x=\dfrac{7}{15}\Rightarrow x=\dfrac{28}{75}\)

Vậy \(x=\dfrac{28}{75}\)

b) \(\left(\dfrac{2}{7}x-1\dfrac{1}{2}x\right):\dfrac{2}{7}=\dfrac{-21}{4}\)

\(\Rightarrow\left(\dfrac{2}{7}x-\dfrac{3}{2}x\right):\dfrac{2}{7}=\dfrac{-21}{4}\)

\(\Rightarrow\dfrac{2}{7}x-\dfrac{3}{2}x=\dfrac{-3}{2}\)

\(\Rightarrow x\left(\dfrac{2}{7}-\dfrac{3}{2}\right)=\dfrac{-3}{2}\)

\(\Rightarrow\dfrac{-17}{14}x=\dfrac{-3}{2}\Rightarrow x=\dfrac{21}{17}\)

Vậy \(x=\dfrac{21}{17}\)

c) \(\dfrac{5}{8}+\dfrac{1}{3}:x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{3}:x=\dfrac{-1}{8}\Rightarrow x=\dfrac{-8}{3}\)

Vậy \(x=\dfrac{-8}{3}\)

d) \(\dfrac{-5}{6}+\dfrac{8}{3}+\dfrac{-29}{6}< x< \dfrac{-1}{2}+2+\dfrac{5}{2}\)

\(\Rightarrow-3< x< 4\)

\(\Rightarrow x\in\left\{-2;-1;0;1;2;3\right\}\) vì x thuộc Z

Vậy \(\Rightarrow x\in\left\{-2;-1;0;1;2;3\right\}\)

Các bạn ơi giúp mk trả lời mấy câu hỏi này với mk đang cần rất gấp ngay bây giờ đây nè!!!!!