Bài 2: Thực hiện phép tính bằng cách hợp lý (nếu có thể) a)(-31)+(50-19)-(150-31) b)25.(45-17)-45.(25-17) c)-1/12+4/3 d)3/5+ -5/20 + 30/75+ -7/4

Đáp án:

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`a,`

`(-31) + (50 – 19) – (150 – 31)`

`= -31 + 50 – 19 – 150 + 31`

`= (-31 + 31) + (50 – 150) – 19`

`= 0 – 100 – 19`

`= -100 – 19`

`= -119`

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`b,`

`25 × (45 – 17) – 45 × (25 – 17)`

`= 25 × 45 – 25 × 17 – 45 × 25 + (-45) × (-17)`

`= [25 × 45 – 45 × 25] + [-25 × 17 – 45 × (-17)]`

`= [25 × (45-45)] + [-25 × 17 + 45 × 17]`

`= [25 × 0] + [17 × (-25 + 45)]`

`= 0 + [17 × 20]`

`= 0 + 340`

`= 340`

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`c,`

`(-1)/12 + 4/3`

`= (-1)/12 + 16/12`

`= (-1 + 16)/12`

`= 15/12`

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`d,`

`3/5 + (-5)/20 + 30/75 + (-7)/4`

`= 3/5 – 1/4 + 2/5 + (-7)/4`

`= (3/5 + 2/5) + ( (-1)/4 + (-7)/4)`

`= 1 + (-2)`

`= 1`