{[270一(45+25)]x12}÷40简便计算{[270一(45+25)]x12}÷40=(270-70*12)÷40=(270-840)÷70=-570÷70=-57/7
{[270一(45+25)]x12}÷40=27/4-7×12/4=27/4-84/4=-57/4=-14又1/4