45 x 399 + 35 x 399 + 20 x 399 
= ( 45 + 35 + 20 ) x 399 
= 100 x 399 
= 39900

 = 399 x (45 + 35 + 20)

 = 399 x 100

 = 39 900

45 x 399 + 35 x 399 + 20 x 399 

= ( 45 + 35 + 20 ) x 399 

= 100 x 399 

= 39900

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

\(=\dfrac{399\times100}{1995\times5}=\dfrac{399\times20}{1995}=\dfrac{7980}{1995}=4\)

56 + 399 + 1 + 4

= (56 + 4) +( 399 + 1)

= 60 + 400 = 460

=312x(17+13)

=312x20

=6240

=312 x ( 17 + 13 )

=312 x 20 

= 6240

a. 312 x 425 + 312 x 574 + 312 = 312 × (425 + 574 + 1)

= 312 × 1000

= 312000

dễ ẹt

bằng 312000 chứ gì

dễ mà dơn giản

a. 312 x 425 + 312 x 574 + 312 = 312 × (425 + 574 + 1)

= 312 × 1000

= 312000

 56+399+1+4

=(56+4)+(399+1)

=60+400

=460

54+6+399+1

=(54+6)+(399+1)

=60+400

=460

56+399+1+4

=(56+4)+(399+1)

=60+400

=460

\(123+132+213+312+321\)

\(=\left(123+312\right)+\left(213+132\right)+321\)

\(=435+345+321\)

\(=\left(435+345\right)+321\)

\(=780+321=1101\)

123+132+213+231+312+321

=(123+321)+(213+132)+321

=435+345+321

=(435+345)+321

=780+321

=1101

123 + 132 + 213 + 231 + 312 + 321

= 123 + 132 + 213 + 312 + 231 + 321

= 255 + 525 + 552

= 780 + 552

= 1232