a, ( 10 + 10 ) - ( 9,34 + 9 , 66 ) 

    = 20 - 19 

    = 1

b, 12 - 2 , 64

   = 9,36

a.= 10 - 9,34 + 10 - 9,66

   = (10 + 10) - (9,66-9,34 )

   =     20       -       0,32             =    19 , 68

b. = 12 -     2,64   =      9,36

a) =9,46
b) =45
c) =20,32
d) =34,9
 

Bài 2. Tính nhanh :
a) 12 – ( 12 – 9,36 )

= 12 - 2,64

= 9,36

b) 72,64 – 18,35 – 9,29

= 54,29 - 9,29

= 45

c) ( 10 – 9,34 ) + ( 10 + 9,66 )

= 0.66 + 19,66

= 20,32

d) 45,83 – 8,46 – 6, 54 + 4,17

= 37,37 - 10,71

= 26,66

1.

( 10 - 9,34 ) + ( 10 - 9,66 )

= 0,66 + 0,34

= 1

12 - ( 12 - 9,36 ) 

= 12 - 2,64

= 9,36

38,52 + 0,302 x 100 - 0,72

= 38,52 + 30,2 - 0,72

= 68,72 - 0,72

= 68

2.

\(1-\left(5\frac{3}{8}+x-7\frac{5}{24}\right):16\frac{2}{3}=0\)

\(1-\left(\frac{43}{8}+x-\frac{173}{24}\right):\frac{50}{3}=0\)

\(\left(\frac{43}{8}+x-\frac{173}{24}\right):\frac{50}{3}=0+1=1\)

\(\left(x-\frac{151}{12}\right):\frac{50}{3}=1\)

\(x-\frac{151}{12}=1\times\frac{50}{3}\)

\(x-\frac{151}{12}=\frac{50}{3}\)

\(x=\frac{50}{3}+\frac{151}{12}\)

\(x=\frac{117}{4}\)

Bài 1

\(\left(10-9,34\right)+\left(10-9,66\right)\)

\(=0.66+0,34=1\)

\(12-\left(12-9,36\right)\)

\(=12-2.64=9,36\)

\(38,52+0,302.100-0,72\)

\(=38,52+30,2-0,72\)

\(=7.6\)

Bài 2

\(1-\left(5\frac{3}{8}+x-7\frac{5}{24}\right):16\frac{2}{3}=0\)

\(1-\left(\frac{43}{8}+x-\frac{173}{24}\right):\frac{50}{3}=0\)

\(\left(\frac{43}{8}+x-\frac{173}{24}\right):\frac{50}{3}=1\)

\(\frac{43}{8}+x-\frac{173}{24}=\frac{3}{50}\)

\(\frac{43}{8}+x=\frac{3}{50}+\frac{173}{24}\)

\(\frac{43}{8}+x=\frac{4361}{600}\)

\(x=\frac{142}{75}\)( gửi lại bài 2 đã ) 

Bài 2 :

\(1-\left(5\frac{3}{8}+x-7\frac{5}{24}\right):16\frac{2}{3}=0\)

\(\left(\frac{15}{8}+x-\frac{35}{24}\right):\frac{32}{3}=1\)

\(\frac{5}{8}+x-\frac{35}{24}=\frac{32}{3}\)

\(\frac{5}{8}+x=\frac{97}{8}\)

\(x=\frac{92}{8}=\frac{23}{2}\)

\(=\dfrac{81048}{307}=264\)

\(=\dfrac{81048}{307}=\dfrac{81048:307}{303:307}=264\)

264

A.-9/10*5/14*1/10*(-9/2)+1/7*(-9/10)

=-9/10*(5/14+1/7)*1/10*(-9/2)

=-9/10*1/2*1/10*(-9/2)

=-9/20*1/10*(-9/10)

=-9/200*-9/10

=81/2000

B. (1999/2011-2011/1999)-(-12/1999-12/2011)

    =1999/2011-2011/1999+12/1999+12/2011

    =(1999/2011+12/2011)-(2011/1999-12/1999)

    = 1-1

    =0

\(\dfrac{16}{24}\times\dfrac{15}{24}=\dfrac{16\times15}{24\times24}=\dfrac{240}{576}=\dfrac{5}{12}\)

\(\dfrac{16}{24}\times\dfrac{15}{24}=\dfrac{5}{12}\)

\(=\dfrac{16\times15}{24\times24}=\dfrac{240}{576}=\dfrac{5}{12}\)

ta có : \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{2016.2017}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{2016}-\frac{1}{2017}\)

\(=1-\frac{1}{2017}\)

\(=\frac{2016}{2017}\)

a) X + 2,14 = 7

               X = 7 - 2,14

               X = 4,86

b) 5,2 x 3,7 - 6,87

    = 19,24 - 6,87

    = 72,37

4x = 7y  và x - y = 12 

Ta có: \(4x=7y=\frac{x}{7}=\frac{y}{4}=\frac{x-y}{7-4}=\frac{12}{3}=4\)

=> \(\frac{x}{7}=4\)                          \(\frac{y}{4}=4\)

=>  \(x=28\)                          \(y=16\)

\(4x=7y\)

\(\Leftrightarrow4x.\frac{1}{28}=7y.\frac{1}{28}\)

\(\Leftrightarrow\frac{x}{7}=\frac{y}{4}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\frac{x}{7}=\frac{y}{4}=\frac{x-y}{7-4}=\frac{12}{3}=4\)

\(\Rightarrow\hept{\begin{cases}x=7.4=28\\y=4.4=16\end{cases}}\)

\(4x=7y\)và x-y=12

4x=7y \(\Rightarrow\)\(\frac{x}{7}=\frac{y}{4}\)

áp dụng tính chất dãy tỉ số bằng nhau ta có:

4x=7y\(\Rightarrow\)\(\frac{x}{7}=\frac{y}{4}\)=\(\frac{x-y}{7-4}=\frac{12}{3}\)=4

Do đó \(\frac{x}{7}=4\Rightarrow x=7\cdot4=28\)

         \(\frac{y}{4}=4\Rightarrow y=4.4=16\)

            7y=4\(\Rightarrow\)y=4.7=28