a) (39 - 2689) + 2689

= 39 + (2689 - 2689)

= 39 + 0

= 39

__

b) - (12 345 - 999) = - (12 345 - 1000+1)

- 12 345 + 12345 + 999 -1000+ 1 = 0

0=0

----

c) (-1312) - (1998 - 1312) 

= (1312 - 1312) - 1998

= 0 - 1998 = -1998

d) (-6955) - 33 - 45 -  (-133)

= -(6955+45) - (33 - 133) 

= -7000 - (-100)

= -7000 + 100 = -6900

e) (-21) - 23 - [16 - (-18) - 18 - 16] + 2144

= -21 - 23 - 16 - 18 + 18 + 16 + 2144

= (16 - 16) + (18 - 18) + (2144 - 21 - 23)

= 0 + 0 + 2100

= 2100

g) (-2020) - 2018 - 2016 - ...-2008

= - [(2020+ 2008): 2 x 7]

= -[(4028): 2 x 7]

= -[2014 x 7]

= - 14098

    345 x 69 - 63 x 345 + 345 x 4

=  345 x ( 69 - 63 + 4 )

=  345 x         10

=        3450

1998 x 497 + 1998 x1 + 1998 x1 + 1998 x1

= 1998 x (497 +1 + 1 + 1 )

=1998 x 500 

= 999000

1998 x 497 + 1998 + 1998 + 1998

= 1998 x 497 + 1998 x 3

= 1998 x ( 497 + 3 )

= 1998 x 500

= 999000

1998 x 497 + 1998 + 1998 + 1998

= 1998 x 497 + 1998 x 3

= 1998 x ( 497 + 3 )

= 1998 x 500

= 999000

a,345x(24+75+1)=345x100=34500

b,(72x1567):8=1567x(72:8)=1567x9=14103

a.345x24+345x75+345

=345x24+345x75+345x1

=345x(24+75+1)

=345x100

=34500

b.(72x1567):8

=1567x(72:8)

=1567x9

=14103

\(34500\)

= 345 x ( 75 + 24 ) + 345

= 34500

=345✖(75+1+24)

=345✖10

=3450

a ) 2 1 5 + 3 4 5 = 2 + 3 + 1 5 + 4 5 = 6

b ) 4 1 2 + 3 4 5 = 4 + 3 + 1 2 + 4 5 = 7 + 13 10 = 8 3 10

Tính nhanh
|-345| + (23 - 345) -|-23|+18 
= 345 + 23 - 345 - 23 +18
= (345-345) + (23-23) +18
= 0 + 0 + 18
= 18
Học tốt !

\(345.57+345.32+3450+345\)

\(=345.57+345.32+345.10+345.1\)

\(=345.\left(57+32+10+1\right)\)

\(=345.100=34500\)

=345*(57+32+3450)

=345*3539

=12220955

\(345\times57+345\times32+3450+345\)

\(=345\times57+345\times32+345\times10+345\times1\)

\(=345\times\left(57+32+10+1\right)\)

\(=345\times100\)

\(=34500\)

~ học tốt ~