Tính hợp lí biểu thức sau: a) − ( − 271 ) − ( 531 + 371 − 731 ) . b) − 138 ⋅ 2 + 125 ⋅ 3 − ( − 138 ⋅ 2 ) + 75 ⋅ 3.

a) \[-\left( { - 271} \right)-\left( {531 + 371-731} \right)\]

\( = 271-531 - 371 + 731\)

\( = \left( {271 - 371} \right) + \left( {-531 + 731} \right)\)

\( = \left( { - 100} \right) + 200\)

\( = 100.\)

b) \( - 138 \cdot 2 + 125 \cdot 3 - \left( { - 138 \cdot 2} \right) + 75 \cdot 3\)

\( = \left[ { - 138 \cdot 2 - \left( { - 138 \cdot 2} \right)} \right] + \left( {125 \cdot 3 + 75 \cdot 3} \right)\)

\( = 0 + 3 \cdot \left( {125 + 75} \right)\)

\( = 0 + 3 \cdot 200\)

\( = 0 + 600\)

\( = 600.\)