Tính nhanh a) 12,7 + 12,7 + 12,7 + 12,7 x 8 – 12,7 b) 81,3 x 99 + 82 – 0,7 c) (100 + 42) x 42 + (200 – 58) x 58 d) 17,8 x 99 + 17 + 0,8 e) 103,7 x 101 – 103 – 0,7 g) 124 x 76 + 12 x 248 h) 12,48 x 3,47 – 3,47 x 2,48 i) 128 x 68 + 16 x 256

Đáp án + Giải thích các bước giải:

Ta có :

`a,12,7+12,7+12,7+12,7.8-12,7`

`=12,7(1+1+1+8-1)`

`=12,7.10`

`=127`

`------------`

`b,81,3.99+82-0,7`

`=81,3.99+(82-0,7)`

`=81,3.99+81,3`

`=81,3(99+1)`

`=81,3.100`

`=8130`

`-------------`

`c,(100+42).42+(200-58).58`

`=142.42+142.58`

`=142(42+58)`

`=142.100`

`=14200`

`--------------`

`d,17,8.99+17+0,8`

`=17,8.99+(17+0,8)`

`=17,8.99+17,8`

`=17,8(99+1)`

`=17,8.100`

`=1780`

`--------------`

`e,103,7.101-103-0,7`

`=103,7.101-(103+0,7)`

`=103,7.101-103,7`

`=103,7(101-1)`

`=103,7.100`

`=10370`

`-------------`

`g,124.76+12.248`

`=124.76+12.2.124`

`=124.76+24.124`

`=124(76+24)`

`=124.100`

`=12400`

`-------------`

`h,12,48.3,47-3,47.2,48`

`=3,47(12,48-2,48)`

`=3,47.10`

`=34,7`

`-------------`

`i,128.68+16.256`

`=128.68+16.2.128`

`=128.68+32.128`

`=128(68+32)`

`=128.100`

`=12800`