a. x x 45 + x x 55 = 1000

x  x (45 + 55) = 1000

x x 100 = 1000

x = 1000 : 100

x =  10

b. 

6 x + 1 2 = 2 6   :   x + 1 2 =   2 6   :   x   =   2 - 1 2 6   :   x     =   3 2 x     =     6   :   3 2 x     =     4

 x x 45 + x x 55 = 1000

      x  x (45 + 55) = 1000

                x x 100 = 1000  

                          x = 1000 : 100

                          x =  10 

x.(45 + 55) = 1000

x. 100 =1000

     x = 1000 : 100 

     x =10

X.45+X.55=1000

X.(45+55)=1000

X=1000:100

X=10

x . 45 + x . 55 = 1000

x . ( 45 + 55 ) = 1000

x . 100 = 1000

x = 1000 : 100

x = 10

Vậy x = 10

6 / x + 1 / 2 = 2

6 / x = 2 - 1 / 2

6 / x = 3 / 2

6 / x = 6 / 4 

=> x = 4

Vậy x = 4

1. x = 10

2. x = 2

...

x . 45 + x . 55 = 1000

x . ( 45 + 55 ) = 1000

x . 100 = 1000

x = 1000 : 100

x = 10

..............................................

a) 399(45+55) / 1995(1996-1991)

=39900 / 9975

=4

b) 

a) \(\frac{399\cdot45+55\cdot399}{1995\cdot1996-1991\cdot1995}\)

\(=\frac{399\cdot\left(45+55\right)}{1995\cdot\left(1996-1991\right)}\)

\(=\frac{399\cdot100}{1995\cdot5}\)

\(=4\)

=))

\(a,\frac{399×\left(45+55\right)}{1995×\left(1996-1991\right)}\)

\(=\frac{39900}{9975}\)

\(=4\)

a) 399(45+55) / 1995(1996-1991)

=39900 / 9975

=4

a) \(\frac{399\cdot45+55\cdot399}{1995\cdot1996-1991\cdot1995}\)

\(=\frac{399\cdot\left(45+55\right)}{1995\cdot\left(1996-1991\right)}\)

\(=\frac{399\cdot100}{1995\cdot5}\)

\(=4\)

=))

b) 1000.1995+1995.996-996

    1000+1000.1994+1994.996

=1000.1995+996.1994

   1000.1995+996.1994

=1

a, X x 45 + X x 55 = 1000

X x (45 + 55) = 1000

X x 100 = 1000

X = 1000 : 100

X = 10

b, \(\frac{6}{x}+\frac{1}{2}=2\)

\(\frac{6}{x}=2-\frac{1}{2}\)

\(\frac{6}{x}=\frac{3}{2}\)

\(\frac{6}{x}=\frac{6}{4}\)

\(x=4\)

a ) \(x\times45+x\times55=1000\)

\(x\times\left(45+55\right)=1000\)

\(x\times100=1000\)

\(x=1000\div100=10\)

b ) \(\frac{6}{x}+\frac{1}{2}=2\)

\(\frac{6}{x}=2-\frac{1}{2}\)

\(\frac{6}{x}=\frac{3}{2}\)

\(=>x=6\div3\times2=4\)

(  ) x 9999 x 9999 x 9999 x ... ( có 1000 số 9999 )  x 38 x 45 x 36 x 25 x 58 x 69 x 245 x 246 x 213 x 222 x 546 x 8312 x 999 x 454 x 9999 x 789 x 2563 x 0 x 25 x 24 x 23 x 26 258 x 256 256 x 256 x 24531 x 55 x ( 45 x 1 + 45 x 2 + 45 x 3 + ... + 45 x 1000 +  45 x 1001 + ... + 45 x 9999 ) = 0 nhé

/HT\

(  ) x 9999 x 9999 x 9999 x ... ( có 1000 số 9999 )  x 38 x 45 x 36 x 25 x 58 x 69 x 245 x 246 x 213 x 222 x 546 x 8312 x 999 x 454 x 9999 x 789 x 2563 x 0 x 25 x 24 x 23 x 26 258 x 256 256 x 256 x 24531 x 55 x ( 45 x 1 + 45 x 2 + 45 x 3 + ... + 45 x 1000 +  45 x 1001 + ... + 45 x 9999 ) =  0

HT

@@@@@@@

  ) x 9999 x 9999 x 9999 x ... ( có 1000 số 9999 )  x 38 x 45 x 36 x 25 x 58 x 69 x 245 x 246 x 213 x 222 x 546 x 8312 x 999 x 454 x 9999 x 789 x 2563 x 0 x 25 x 24 x 23 x 26 258 x 256 256 x 256 x 24531 x 55 x ( 45 x 1 + 45 x 2 + 45 x 3 + ... + 45 x 1000 +  45 x 1001 + ... + 45 x 9999 ) = 0 

k cần

399 x 45 x 399 : 1995 x 1996 - 1991 x 1995

= 3195591

1996 x 1995 - 996 : 1000 + 1996 x 1994

= 7962043.004

Làm lại nhé:

399 x 45 + 55 x \(\frac{399}{1995}\) x 1996 - 1991 x 1995

= -3932134

1996 x 1995 - \(\frac{996}{1000}\)+ 1996 x 1994

= 7962043.004

Đề bài sai hay sao ấy!