Question

tính nhanh 

a) 21 . 78 + 21 . 23 -21

b) 57 . 64 - 57 .3 + 39.57

c) 47.29 - 13 .29 - 24.29

d) 12.53  + 53 .172 - 53. 84

e) 24.42 - 35 .24 - 24.7

Answer 1

`a) 21 . 78 + 21 . 23 -21`

`=21. ( 78+23-1)`

`=21.100`

`=2100`

`b) 57 . 64 - 57 .3 + 39.57`

`=57.(64 -3+39)`

`=57. 100`

`=5700`

`c) 47.29 - 13 .29 - 24.29`

`=(47-13-24).29`

`=10.29`

`=290`

`d) 12.53  + 53 .172 - 53. 84`

`= 53.(12+172-84)`

`=53.100`

`=53100`

`e) 24.42 - 35 .24 - 24.7`

`= 24.(42-35-7)`

`=24.0`

`=0`

Answer 2

a) 21 . 78 + 21 . 23 - 21

= 21( 78 + 23 - 1)

=21 .100

= 2100

b) 57 . 64 - 57 . 3 + 39 . 57

= 57 ( 64 - 3 + 39)

= 57 . 100

=5700

 

Answer 3

cho mik hỏi dấu . là x hay . ạ

 

Answer 4

nếu cậu thật sự gấp tớ sẽ làm cho đừng đăng lại nhé

Answer 5

\(a,21.78+21.23-21=21.\left(78+23\right)-21=21.101-21=2121-21=2100\)

\(b,57.64-57.3+39.57=57.\left(64-3+39\right)=57.100=5700\)

\(c,47.29-13.29-24.29=29.\left(47-13-24\right)=29.10=290\)

\(d,12.53+53.172-53.84=53.\left(12+172-84\right)=53.100=5300\)

\(e,24.42-35.24-24.7=24.\left(42-35-7\right)=24.0=0\)