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

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1. 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 `

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2. `a,` `5/9-11/18`

   `=10/18-11/18`

   `={-1}/18`

   `b,` `1/12+3/4-5/8`

   `=2/24+18/24-15/24`

   `=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`

   `=3/8`

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