4.23-(4.23-2.56)简便计算解：采用结合律，原式=4.23-(4.23-2.56)=4.23-4.23+2.56=2.56
4.23-4.23+2.56=2.56
awake to the terror of a bad sore throat; and
4.23-(4.23-2.56)=4.23-4.23+2.56=2.56
