15.7+12.54-0.46-0.3=16-0.3+(13-0.46)-0.46-0.3=16+13-(0.46+0.46+0.3+0.3)=29-1.52=27.48
先用15.7+12.54=28.24.再看0.46+0.3=0.76,最后用28.24-0.76=27.48.得到27.48
