Tính A= 1/17+ 1/170 + 3/70 + 2/35 + 1/20

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1. `A= 1/20 + 2/35 + 3/70 + 1/170 + 1/17`

   `A= 1/4.5 + 2/5.7 + 3/7.10 + 1/170 + 1/17`

   `A= 1/4 – 1/5 + 1/5 – 1/7 + 1/7- 1/10 + 1/170 + 1/17`

   `A= 1/4 – 1/10 + 1/170 + 1/17`

   `A= 3/20 + 1/170 + 1/17`

   `A= 53/240 + 1/17`

   `A=73/340`

   Vậy `A= 73/340`

    

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2. `A= 1/17+ 1/170 + 3/70 + 2/35 + 1/20`

   `⇔A=(140)/(2380)+(14)/(2380)+(102)/(2380)+(136)/(2380)+(119)/(2380)`

   `⇔A=(140+14+102+136+119)/(2380)`

   `⇔A=(511)/(2380)`

   `⇔A=(73)/(340)`

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