=12.71-2.56-2.44+1.83=12.71-（2.56+2.44）+1.83=12.71-5+1.83=9.54
(12.17-2.56)-(2.44-1.83)=12.17-2.56-2.44+1.83=(12.17+1.83)-(2.56+2.44)=14-5=9
