=(4x0.25)x(2x0.5)

=1x1=1

địt con mẹ mày lên

\(\dfrac{1}{3}\)-\(\dfrac{2}{15}\)+\(\dfrac{14}{15}\)=\(\dfrac{3}{15}\)-\(\dfrac{2}{15}\)+\(\dfrac{14}{15}\)

=\(\dfrac{13}{15}\)

\(\dfrac{3}{5}\)+4-\(\dfrac{6}{7}\)=\(\dfrac{3}{5}\)+\(\dfrac{20}{5}\)-\(\dfrac{6}{7}\)=\(\dfrac{23}{5}\)-\(\dfrac{6}{7}\)=\(\dfrac{161}{35}\)-\(\dfrac{30}{35}\)=\(\dfrac{131}{35}\)

A)\(\dfrac{7}{20}-\left(\dfrac{5}{8}-\dfrac{2}{5}\right)\)

\(=\dfrac{7}{20}-\left(\dfrac{25}{40}-\dfrac{16}{40}\right)\)

\(=\dfrac{7}{20}-\dfrac{9}{40}\)

\(=\dfrac{14}{40}-\dfrac{9}{40}=\dfrac{5}{40}=\dfrac{1}{8}\)

B) \(\dfrac{5}{6}+\left(\dfrac{5}{9}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{6}+\left(\dfrac{20}{36}-\dfrac{9}{36}\right)\)

\(=\dfrac{5}{6}+\dfrac{11}{36}\).

\(=\dfrac{30}{36}+\dfrac{11}{36}=\dfrac{41}{36}\)

C) \(\dfrac{9}{10}-\left(\dfrac{2}{5}-\dfrac{3}{10}\right)+\dfrac{7}{20}\)

\(=\dfrac{9}{10}-\left(\dfrac{4}{10}-\dfrac{3}{10}\right)+\dfrac{7}{20}\)

\(=\dfrac{9}{10}-\dfrac{1}{10}+\dfrac{7}{20}\)

\(=\dfrac{18}{20}-\dfrac{2}{20}+\dfrac{7}{20}=\dfrac{23}{20}\)

a: =7/20-5/8+2/5

=14/40-25/40+16/40

=5/40=1/8

b: =5/6+5/9-1/4

=30/36+20/36-9/36

=41/36

c: =9/10-2/5+3/10+7/20

=12/10-2/5+7/20

=7/20+6/5-2/5

=7/20+4/5

=7/20+16/20

=23/20

a) \(\dfrac{2^6\cdot5^5}{10^5}\)

\(=\dfrac{2^6\cdot5^5}{2^5\cdot5^5}\)

\(=2\)

b) \(\dfrac{3^6\cdot5^7}{15^6}\)

\(=\dfrac{3^6\cdot5^7}{3^6\cdot5^6}\)

\(=5\)

a) (2/5 x 25/29) + (3/5 x 25/29)
= (50/145) + (75/145)
= 125/145

b) (5/2 x 3/7) - (3/14 : 6/7)
= 15/14 - (3/14 x 7/6)
= 15/14 - 1/2
= (30/28) - (14/28)
= 16/28
= 4/7

c) (15/4 : 5/12) - (6/5 : 11/15)
= (15/4 x 12/5) - (6/5 x 15/11)
= 180/20 - 90/55
= 9 - 18/11
= (99/11) - (18/11)
= 81/11
= 7 4/11

a) (2/3) + (20/21 x 3/2 x 7/5)
= 2/3 + (60/210)
= 2/3 + 2/7
= (14/21) + (6/21)
= 20/21

b) (5/17 x 21/32 x 47/24 x 0)
= 0

c) (11/3 x 26/7) - (26/7 x 8/3)
= (286/21) - (208/21)
= 78/21
= 3 9/21
= 3 3/7

a) (25/8) : x = 5/16
=> (25/8) x (16/5) = x
=> 4 = x

b) x + (7/15) = 6/15
=> x = (6/15) - (7/15)
=> x = -1/15

c) x : (28/49) = 7/12
=> x x (49/28) = 7/12
=> x = (7/12) x (28/49)
=> x = 1/2

a) 6 x x = (5/8) : (3/4)
=> 6x = (5/8) x (4/3)
=> 6x = 20/24
=> 6x = 5/6
=> x = (5/6) / 6
=> x = 5/36

câu,b,không,đủ,thông,tin,nhan,bạn.

= 13/30

bài 1 : 

B=15-3x-3y

a) x+y-5=0 

=>x+y=-5

B=15-3x-3y <=> B=15-3(x+y)

Thay x+y=-5 vào biểu thức  B ta được :

B=15-3(-5)

B=15+15

B=30

Vậy giá trị của biểu thức B=15-3x-3y tại x+y+5=0 là 30

b)Theo đề bài ; ta có :

B=15-3x-3.2=10

15-3x-6=10

15-3x=16

3x=-1

\(x=\frac{-1}{3}\)

Bài 2:

a)3x²-7=5

3x²=12

x²=4

x=\(\pm2\)

b)3x-2x²=0

=> 3x=2x²

=>\(\frac{3x}{x^2}=2\)

=>\(\frac{x}{x^2}=\frac{2}{3}\)

=>\(\frac{1}{x}=\frac{2}{3}\)

=>\(3=2x\)

=>\(\frac{3}{2}=x\)

c) 8x² + 10x + 3 = 0

=>\(8x^2-2x+12x-3=0\)

\(\Rightarrow\left(2x+3\right)\left(4x-1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x+3=0\\4x-1=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}2x=-3\\4x=1\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{-3}{2}\\x=\frac{1}{4}\end{cases}}}\)

vậy \(x\in\left\{-\frac{3}{2};\frac{1}{4}\right\}\)

Bài 5 đề  sai  vì  |1| không thể =2

10.213

11. 2 giờ 55 phút

12. 4 ngày 21 giờ

13.

a: 6,008

b: 4500

c: 5,628

d: 4,009

14.

a,8579 cm2

b,32,04 m2

c,187200m2

d,5,017 tấn