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`
