Tính nhanh: A= 3/4 x 2/5 + 3/8 x 7/13 + 3/5 x 3/4 + 3/13 x 6/8

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1. `A= 3/4 xx 2/5 + 3/8 xx 7/13 + 3/5 xx 3/4 + 3/13 xx 6/8`

   `A= 3/4 xx ( 2/5 + 3/5) + 3/8 xx 7/13 + 3/13 xx 3/4`

   `A= 3/4 xx . 1 + 3/4 xx 3/13 + 7/13 xx 3/8`

   `A=  3/4 ( 1 + 3/13) + 7/13 xx 3/8`

   `A= 3/4 xx 16/13 + 7/13 xx 3/8`

   `A= 12/13 + 7/13 xx 3/8`

   `A=12/13 + 21/104`

   `A= 9/8`

   Vậy `A= 9/8`

    

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2. Đáp án + Giải thích các bước giải:

   A= 3/4 x 2/5 + 3/8 x 7/13 + 3/5 x 3/4 + 3/13 x 6/8

     = (3/4 x 2/5 + 3/5 x 3/4) + (3/8 x 7/13 +3/13 x6/8)

     = 3/4 x (2/5 +3/5) + 3/8 x(7/13 + 3/13 x2)

     =3/4 +3/8

     = 9/8

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