2/25.

C)-1/4+-5/17.[1/3:20/17.

5.tính nhanh a)-3/7+5/13+-4/7

B) 5/9+7/12+4/9

C) 9/10.-7/8+9/10.-1/8

D 7/19.8/11+7/19.3/11+12/19.

6 . tim x

A) X+1/7=-2/3.

B)5/9+7/12+4/9.

C)-1/3.x5/7.

D)x:-5/9=9/10

E)x/3=2/3+-1/7.

7)qua da hau nang bao nhieu kilogam neu biet 2/3qua dau nang .1, 2 phan 3 kg?

8biet ti so phan tram nUoc tong dua cHuot la 97,2%tinh luong nuoc trong 4 kg dua chuot.

Bài 1:Tìm x biết Bài 2:So sánh

a, \(x+\frac{1}{2}=\frac{3}{8}.\frac{4}{5}\) a, \(A=\frac{10^{10}-1}{10^{11}-1}vaB=\frac{10^9-1}{10^{10}-1}\)

b, \(\frac{5}{16}:x-\frac{1}{4}=\frac{5}{8}\) b, B =\(\frac{10^{10}}{10^{10}+1}vaB=\frac{10^{10}+1}{10^{10}+2}\)

c, \(\frac{-1}{4}.x+\frac{3}{7}.x=2\)

d, \(\frac{22}{9}-\left(x+\frac{1}{2}\right)^2=\frac{7}{3}\)

e, \(\left|\frac{1}{4}-x\right|+5\frac{1}{8}=6\frac{1}{8}\)

bài 2 tìm x

a,\(\frac{-2}{3}.x+\frac{1}{5}=\frac{3}{10}\)

b,\(\left|x\right|-\frac{3}{4}=\frac{5}{3}\)

c,\(\frac{2}{3}.x-\frac{1}{2}=\frac{1}{10}\)

d,\(\frac{3}{5}+\frac{4}{9}:x=\frac{2}{3}\)

e,\(\left|x+75\%\right|=2\frac{1}{5}\)

i,\(\left(x+\frac{1}{2}\right).\left(\frac{2}{3}-2.x\right)=0\)

k,\(\frac{4}{7}.x-\frac{2}{3}=\frac{1}{5}\)

l,\(\frac{2}{3}.x-\frac{3}{2}.x=\frac{5}{12}\)

m,\(\left|2.x-\frac{1}{3}\right|+\frac{5}{6}=1\)

n,\(\frac{1}{3}-\frac{7}{8}.x=\frac{1}{3}\)

11,\(\frac{x+2}{5}=\frac{7}{12}-1\frac{1}{4}\)

12,\(\left(2\frac{4}{5}.x-50\right):\frac{2}{3}=51\)

13,\(\frac{2}{5}+\frac{3}{5}.\left(3.x-3,7\right)=-\frac{53}{10}\)

14,\(\frac{7}{9}:\left(2+\frac{3}{4}.x\right)+\frac{5}{9}=\frac{23}{27}\)

Câu 1 : Tính

a) \(\frac{2}{3}\)+\(\frac{1}{3}\)x ( \(\frac{-4}{9}\)+\(\frac{5}{6}\)) : \(\frac{7}{12}\)

b) S = \(\frac{1}{2}\)x \(\frac{1}{3}\)+\(\frac{1}{3}\)x\(\frac{1}{4}\)+\(\frac{1}{4}\)x\(\frac{1}{5}\)+\(\frac{1}{5}\)x\(\frac{1}{6}\)+\(\frac{1}{6}\)x\(\frac{1}{7}\)+\(\frac{1}{7}\)x\(\frac{1}{8}\)+\(\frac{1}{8}\)x\(\frac{1}{9}\)

c) A = \(\frac{5}{5.7}\)+\(\frac{5}{7.9}\)+...+\(\frac{5}{59.61}\)

d) M = \(\frac{3}{4}\)x\(\frac{8}{9}\)x\(\frac{15}{16}\)x\(\frac{24}{25}\)x...x\(\frac{99}{100}\)

e) N = \(\frac{1}{2}\)x\(\frac{-2}{3}\)x\(\frac{3}{4}\)x\(\frac{-4}{5}\)x\(\frac{5}{6}\)x\(\frac{-6}{7}\)x...x\(\frac{-98}{99}\)x\(\frac{99}{100}\)

[ Các bạn trả lời cách tính nhanh mà đúng nhá :)) ]

[ Cảm ơn các bạn nhiều <3 ]

bài 1 tìm x,y,z 

a,\(\frac{x}{10}\)=\(\frac{y}{15}\),x=\(\frac{7}{2}\)và x+2y-3z=20

b,2x=3y,49=57 và 4x-3y+5z=7

c,\(\frac{2x}{3}\)=\(\frac{3y}{4}\)=\(\frac{47}{5}\)và x+y+z=49

2 tìm x trong các tỉ lệ thức sau

a, \(\frac{x-3}{x+5}=\frac{5}{7}\)

 b,\(\frac{7}{x-1}\)\(=\frac{x+1}{9}\)

c \(\frac{x+4}{20}=\frac{5}{x+4}\)

d,\(\frac{x-1}{x+2}=\frac{x-2}{x+3}\)

bài 3: tìm các số x,y,z

a,\(\frac{x}{y}=\frac{7}{10}=\frac{z}{9}\)

b,\(\frac{x}{y}=\frac{9}{7};\frac{y}{z}=\frac{7}{3}\) và x-y+z=-15

c,\(\frac{x}{y}=\frac{7}{20};\frac{y}{z}=\frac{5}{8}\)và 2x+5y-2z=100

bài 4 tìm các số x,y,z

a,5x=8y=20z và x-y-z=3 

b ,\(\frac{6}{11}x=\frac{9}{2}y=\frac{18}{5}z\)và -x+y+z=-120

bài 5 tìm x,y,z biết

và xyz=20

bài 6 tìm x,y,z biết

\(\frac{x}{5}=\frac{y}{7}=\frac{z}{3}\)và x²  + y² -z² =585