A) 240 - (127 + x) = 90

⇒ 127 + x = 240 - 90 

⇒ 127 + x = 150

⇒ x = 150 - 127

⇒ x = 23

B) 65 + (5x + 20) : 2 = 125

⇒ (5x + 20) : 2 = 125 - 65

⇒ (5x + 20) : 2 = 60

⇒ 5x + 20 = 120

⇒ 5x = 120 - 20 

⇒ 5x = 100

⇒ x = 100 : 5

⇒ x = 20

C) x ϵ B(8) và 24 ≤ x <45

Mà: B(8) = { 0;8;16;24;32;40;48;...}

⇒ x ϵ { 24; 32; 40} 

\(240-\left(127+x\right)=90\)

\(127+x=150\)

\(x=23\)

\(65+\left(5x+20\right):2=125\)

\(\left(2x+20\right):2=60\)

\(2x+20=120\)

\(2x=100\)

\(x=50\)

\(x=\left\{a\in N,a\notin32,a\notin40\text{|}24< a< 45\right\}\)

a ) 2 x 3 x 4 x 8 x 50 x 25 x 125

  = 3 x 2 x 50 x 4 x 25 x 8 x 125

  = 3 x ( 2 x 50 ) x ( 4 x 25 ) x ( 8 x 125 )

  = 3 x 100 x 100 x 1000

  = 30000000

b ) 45 x 128 - 90 x 64

  = 45 x ( 2 x 64 ) - 90 x 64

  = ( 45 x 2 ) x 64 - 90 x 64

  = 90 x 64 - 90 x 64

  = 0

a) = (2.50).(4.25).(8.125).3=100.100.1000.3=30000000

b)45.128-90.64=45.128-45.2.64

=45.128-45.128

=0

a) 2 x 3 x 4 x 8 x 50 x 25 x 125
=  (25 x 4) x (50 x 2) x (125 x 8) x 3
=  100 x 100 x 1000 x 3
=  30000000

b) 45 x 128 - 90 x 64
=  45 x 128 - 45 x 2 x 64
=  45 x 128 - 45 x 128
=  0

1) 1996 + 3992 + 5988 + 7984 
= 1996 x 1 + 1996 x 2 + 1996 x 3 + 1996 x 4 
= 1996 x ( 1 + 2 + 3 + 4) 
= 1996 x 10 = 19960 
2) 2 x 3 x 4 x 8 x 50 x 25 x 125 
= 3 x (2 x 50) x (4 x 25) x (8 x 125) 
= 3 x 100 x 100 x 1000 
= 30.000.000 
3(45 x 46 + 47 x 48) x (51 x 52 - 49 x 48) x (45 x 128 - 90 x 64) 
x (1995 x 1996 + 1997 x 1998) 
Ta thÊy : 45 x 128 - 90 x 64 
= 45 x 2 x 64 - 90 x 64 
= 90 x 64 - 90 x 64 
= 0 

1) 1996 + 3992 + 5988 + 7984 
= 1996 x 1 + 1996 x 2 + 1996 x 3 + 1996 x 4 
= 1996 x ( 1 + 2 + 3 + 4) 
= 1996 x 10 = 19960 
2) 2 x 3 x 4 x 8 x 50 x 25 x 125 
= 3 x (2 x 50) x (4 x 25) x (8 x 125) 
= 3 x 100 x 100 x 1000 
= 30.000.000 
3(45 x 46 + 47 x 48) x (51 x 52 - 49 x 48) x (45 x 128 - 90 x 64) 
x (1995 x 1996 + 1997 x 1998) 
Ta thÊy : 45 x 128 - 90 x 64 
= 45 x 2 x 64 - 90 x 64 
= 90 x 64 - 90 x 64 
= 0 

L I K E NHÁ BẠN^^

1  1996 + 3992 + 5988 +7984

= [ 1996 + 7984 ] + [ 5988 + 3392 ]

=           9980      +            9380

=                         19360

a, Ta có :

1996 + 3992 + 5988 + 7984

= 1 x 1996 + 2 x 1996 + 3 x 1996 + 4 x 1996

= (1 + 2 + 3 + 4) x 1996

= 10 x 1996

= 19960

b, 2 x 3 x 4 x 8 x 50 x 25 x 125

= 3 x 2 x 4 x 50 x 8 x 25 x 125

= 3 x (2 x 50) x (4 x 25) x (8 x 125)

= 30 000 000.

c, Ta nhận thấy :

45 x 128 – 90 x 64 = 45 x (2 x 64) – 90 x 64

= (45 x 2) x 64 – 90 x 64

= 90 x 64 – 90 = 0

Trong 1 tích có 1 thừa số bằng 0. Vậy tích đó bằng 0, tức là :

(45 x 46 + 47 x 48) x (51 x 52 – 49 x 48) x (45 x 128 – 90 x 64) x (1995 x 1996 + 1997 x 1998) = 0

4 × 125 × 25 × 8

= (4 × 25) × (125 × 8)

= 100 × 1000

= 100 000

2 × 8 × 50 × 25 × 125

= (2 × 50) × (8 × 125) × 25

= 100 × 1000 × 125

= 12 500 000

2 × 3 × 4 × 5 × 50 × 25

= (2 × 50) × (4 × 25) × (3 × 5)

= 100 × 100 × 15

= 150 000

25 × 20 × 125 × 8 - 8 × 20 × 5 × 125

= 8 × 125 × 20 × (25 - 5)

= 1000 × 20 × 20

= 400 000

- (25 x 4) x (125 x8)=100 x 1000 =100000

- (50 x 2) x (8 x 125) x 25=100 x 1000 x 25 =2500000

- (2 x 50 ) x (4 x 25) x (3 x5)=100 x 100 x 15=150000

- 25 x 20 x125 x 8 - 5

= (20 x 5) x (125 x 8) -25=100 x 1000 -5 =100000 - 5 =99995

4 *125*25*8

=4*25*125*8

=100*1000

=100000

2*8*50*25*125

=2*50*8*125*25

=100*1000*25

=2500000

2*3*4*5*50*25

=2*50*4*25*3*5

=100*100*15

=150000

25*20*125*8-8*20*5*125

=25*4*5*125*8-8*125*20*5

=100*1000*5-1000*100

=500000-100000

=400000

=

\(4.125.25.8\)

\(=\left(4.25\right).\left(125.8\right)\)

\(=100.1000\)

\(=100000\)

\(2.3.4.5.50.25\)

\(=\left(2.50\right).\left(4.25\right).\left(3.4.5\right)\)

\(=100.100.60\)

\(=10000.60\)

\(=600000\)

\(2.8.50.25.125\)

\(=\left(2.50\right).\left(8.125\right).25\)

\(=100.1000.25\)

\(=100000.25\)

\(=2500000\)

Bài 1: 

\(101\cdot125+101\cdot25-101\cdot50\)

\(=101\cdot\left(125+25-50\right)\)

\(=101\cdot100\)

\(=10100\)

Bài 2: 

\(76\cdot115+56\cdot24+59\cdot24\)
\(=76\cdot115+24\cdot\left(56+59\right)\)

\(=76\cdot115+24\cdot115\)

\(=115\cdot\left(76+24\right)\)

\(=115\cdot100\)

\(=11500\)

5:

a: =>15x=165

=>x=11

b: =>x(x+1)/2=55

=>x^2+x=110

=>x=10

4: =>7x=56

=>x=8

Bài 1:

101•125+101•25+101•50

= 101•(125+25-50)

=101•100

=10100

Bài 2:

76•115+56•24+59•24

= 76•115+24•(56+59)

= 76•115+24•115

= 115•(76+24)

= 115•100

= 11500

1 : Tính nhanh:

a) 2376 + 3425 - 376 - 425 = ( 2376 - 376 ) + ( 3425 - 425 )

                                       = 2000 + 3000

                                       = 5000

b)4638 - 2437 + 5362 - 7563 = 2210 + ( - 2210 )

                                          = 0

c) 45 + 45 + 45 + 45 + 15 + 15 + 15 + 15

  = 45 x 4 + 15 x 4

 = ( 45 + 15 ) x 4

 = 60 x 4

 = 240

d) 4 x 125 x 25 x 8 = ( 4 x 25 ) x ( 125 x 8 )

                            = 100 x 1000

                            = 100000

e) 2 x 8 x 50 x 25 x 125 = ( 2 x 50 ) x ( 8 x 125 ) x 25

                                   = 100 x 1000 x 25

                                   = 100000 x 25

                                   = 2500000

2 : Tính nhanh bằng 2 cách:

C1 : 125 + 125 + 125 + 125 - 25 - 25 - 25 - 25

    = ( 125 - 25 ) + ( 125 - 25) + ( 125 - 25 ) + ( 125 - 25 )

    =100 + 100 + 100 + 100 

    = 100 x 4 

    = 400

C2 : 125 + 125 + 125 + 125 - 25 - 25 - 25 - 25

     = 125 x 4 - 25 x 4

     = ( 125 - 25 ) x 4

     = 100 x 4

     = 400

1.

a. 5000
b. 0

c. 240

d. 100000

e. 2500000

2.

400

1: Tính nhanh:

a, 2376 + 3425 - 376 - 425

 = ( 2376 - 376 ) + ( 3425 - 425 )

 = 2000 + 3000

 = 5000.

b, 4638 - 2437 + 5362 - 7563

 = 2210 + (-2210)

 = 0.

c, 45 + 45 + 45 + 45 + 15 + 15 + 15 + 15 + 15

 = ( 45 + 15 ) +  ( 45 + 15 ) +  ( 45 + 15 ) +  ( 45 + 15 ) 

 = 60 + 60 + 60 + 60

 = 240.

d, 4 x 125 x 25 x 8 

 = ( 4 x 25 ) x ( 125 x 8 )

 = 100 x 1000

 = 100000.

e, 2 x 8 x 50 x 25 x 125

 = ( 2 x 50 ) x ( 8 x 125 ) x 25

 = 100 x 1000 x 25

 = 2500000.

2: Tính nhanh bằng hai cách:

  125 + 125 + 125 + 125 - 25 - 25 - 25- 25

= ( 125 - 25 ) + ( 125 - 25 ) + ( 125 - 25 ) + ( 125 -25 )

= 100 + 100 + 100 + 100

= 400.