a, 5/9 – 11/18 b, 1/12 + 3/4 – 5/8 c, 2/3 . 7/9 + 2/3 . 1/9 – 2/3 . 17/9 d, 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 help

Đáp án:

`↓ ↓ ↓ ↓ `

Giải thích các bước giải:

a,

`5/9 – 11/18 = 10/18 – 11/18 = -1/18`

b,

` 1/12 + 3/4 – 5/8 = 2/24 + 18/24 – 15/24 = 20/24 -15/24 = 5/24`

c)

`2/3 . 7/9 + 2/3 . 1/9 – 2/3 . 17/9 = 2/3 . (7/9 + 1/9 – 17/9 ) = 2/3 . 25/9 = 50/27`

d, 

 `1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56`

`= 1/ 2.3 + 1/ 3.4 + 1/4.5 + 1/ 5.6 + 1/ 6.7 + 1/7.8`

`=1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + 1/5 – 1/6 + 1/6 – 1/7 + 1/7 -1/8`      

 `= 1/2 – 1/8 `

` = 4/8 – 1/8`

` = 3/8 `