Bài 1:

1: 2155-(174+2155)+(-68+174)

=2155-174-2155-68+174

=(2155-2155)+(-174+174)-68

=0+0-68

=-68

2: \(-25\cdot72+25\cdot21-49\cdot25\)

\(=25\left(-72+21-49\right)\)

\(=25\cdot\left(-100\right)=-2500\)

3: \(35\cdot\left(14-23\right)-23\cdot\left(14-35\right)\)

\(=35\cdot14-35\cdot23-23\cdot14+23\cdot35\)

\(=35\cdot14-23\cdot14=14\cdot12=168\)

4: \(8154-\left(674+8154\right)+\left(-98+674\right)\)

=8154-674-8154-98+674

=(8154-8154)+(674-674)-98

=0+0-98

=-98

5: \(-25\cdot21+25\cdot72+49\cdot25\)

\(=25\left(-21+72+49\right)\)

\(=25\cdot100=2500\)

6: \(27\cdot\left(13-16\right)-16\left(13-27\right)\)

\(=27\cdot13-27\cdot16-16\cdot13+16\cdot27\)

\(=27\cdot13-16\cdot13=13\cdot\left(27-16\right)=13\cdot11=143\)

7: -1911-(1234-1911)

=-1911-1234+1911

=-1234

8: \(156\cdot72+28\cdot156\)

\(=156\cdot\left(72+28\right)\)

\(=156\cdot100=15600\)

Đề có đúng không bạn?

13567 -  -12 = 13579

\(=\left[\left(-3\right)+\left(-7\right)\right]+\left[\left(-250\right)+250\right]\\ =-10+0=-10\)

=-10

1; (15 + 22) + (135 - 15 - 22)

= 15 + 22  + 135 - 15  - 22

= (15  - 15) + (22 - 22) + 135

= 0 + 0 + 135

= 135 

100 - 99 + 98 - 97 + ... + 4 - 3 + 2 - 1

= 1 + 1 + ... + 1 + 1

= 1 x 50

= 50

(-12)+(-13)+33+(-11)=-25+22=-3

Giair từng bước nha bạn .

-24 ( - 3 - 7 ) -  7 (-24 -3 ) = 429

=429 nha bn

Bài 2: Tính 1 cách hợp lý:

  250.1476.4

=(250.4).1476

= 1000  .1476

=    1476000 

  189 . 509 – 189 . 409

= 189 . (509 – 409)

= 189 . 100 

= 189 000

bạn viết cách ra