1 tính bằng cách hợp lí a) 3/7 x 8/11 x 7/3 b) 4/15 x 3/8 + 4×15 x 3/8 c) 7/5 x 1/2 – 3/5 x 1/2

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1. Đáp án:

    `a) 3/7 × 8/11 × 7/3 `

   `=(3/7×3/7)×8/11`

   `=1×8/11`

   `=8/11`

   `b) 4/15 ×3/8 + 4×15 × 3/8`

   `=3/8×(4/15+60)`

   `=3/8×904/15`

   `=113/5`

   `c)7/5 ×1/2 – 3/5 × 1/2`

   `=1/2×(7/5-3/5)`

   `=1/2×4/5`

   `=2/5`

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2. a) 3/7 x 8/11 x 7/3 

   = 3/7 x 7/3 x 8/11

   = 1 x 8/11

   = 8/11

   b) 4/15 x 3/8 + 4×15 x 3/8

   = 4/15 x 3/8 + 60 x 3/8

   = 3/8 x (4/15 + 60)

   = 3/8 x 904/15

   = 113/5

   c) 7/5 x 1/2 – 3/5 x 1/2

   = (7/5 – 3/5) x 1/2

   = 4/5 x 1/2

   = 2/5

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