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.

(36 × 27) : 3 = 36 × (27 : 3)

= 36 × 9

= 324

--------

(125 × 15) : 5

= 125 × (15 : 5)

= 125 × 3

= 375

--------

(15 × 12) : 9

= (5 × 3 × 12) : 9

= 5 × (36 : 9)

= 5 × 4

= 20

--------

450 : (3 × 5)

= 450 : 15

= 30

--------

(45 × 63) : 9

= 45 × (63 : 9)

= 45 × 7

= 40 × 7 + 5 × 7

= 280 + 35

= 315

a: \(\dfrac{\left(36\cdot27\right)}{3}=36\cdot\dfrac{27}{3}=36\cdot9=324\)

b: \(\dfrac{\left(125\cdot15\right)}{5}=125\cdot\dfrac{15}{5}=125\cdot3=375\)

c: \(\dfrac{\left(15\cdot12\right)}{9}=\dfrac{3\cdot3\cdot4\cdot5}{9}=4\cdot5=20\)

d: \(\dfrac{450}{3\cdot5}=\dfrac{450}{15}=30\)

e: \(\dfrac{45\cdot63}{9}=\dfrac{45}{9}\cdot63=63\cdot5=315\)

a)  x + 125 - 45 + (12+23) = 40

=>   x + 125 - 45 + 35 = 40

=>   x + 115 = 40

=>   x = 40 - 115

=>   x = -75

b) x * 12 = (45 + 45)

=>   x * 12 = 90

=>   x = 90 : 12

=>   x = 7,5

x + 125 - 45 + ( 12 + 23 ) = 40

=> x + 125 +( -45) + 35 = 40

=> x + 80 +35 = 40

=> x + 115 = 40

=> x = -75

x * 12 = ( 45 + 45 )

=> x * 12 = 90 

=> x = 90 : 12 

=> x = 15/2 = 7.5

a) x + 125 - 45 + (12 + 23) = 40

   x + 125 - 45 + 35          = 40

   x                                 = 40 - 35 + 45 - 125

   x                                 = - 65

b) x * 12 = 45 + 45

    x * 12 = 90

    x        = 90 : 12

    x        = 7,5

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

a) 125.3+125.125.6

=125.3+125.750

=125.(3+750)

=125.753

=94125

b) (245.99+245)-(145.101-145)

=(245.(99+1))-(145.(101-1))

=245.100-145.100

=(245-145).100

=100.100

=10000

c) 154.(28+52)-45.(26+54)

=154.80-45.80

=(154-45).80

=109.80

=8720

a) 125x3+125+125x6

=125x(3+1+6)

=125x10

=1250

b) (245x99+245)-(145x101-145)

=(245x99+245)-(145x100)

=(245x100)-14500

=24500-14500

10000

c) 154x80-45x80

=80x(145-45)

=80x100

=8000

a, 125 x 3 + 125 x 125 x 6

=125 x 3 + 125 x 750

=125 x( 3+750)

=125 x753

=94125

b, ( 245 x 99 + 245 ) - ( 145 x 101 - 145 )

=[245 x ( 99+1 )] - [145 x ( 101-1 )]

=( 245 x 100 ) - ( 145 x 100 )

=24500 - 14500

=10 000

c, 154 x ( 28 + 52 ) - 45 x ( 26 + 54 )

=154 x 80 - 45 x 80

=(154-45)x80

=109 x80

=8720

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

Ta có: 125/100 = x/45

=> 100x = 125.45

=> 100x = 5625

=> x = 5625: 100

=> x = 225/4

Vậy x = 225/4

(45/5+5/5)×x=125×4

10×x=500

X=500÷10

X=50

A=[(38+17)+125]+29

A=175+29

A=204

B=312.3

B=936

C=1+1+1+1+1

C=5

D=(125:5).(36:9)

D=25.4

D=100