二分之(x-1)=二分之（十二-x） x-1=12-x 2x=13 x=6.5 2.2×0.25×8×【12.7-（7.25+4.5）】÷3.8 =2.2×2×（12.7-11.75）÷3.8 =4.4×0.95÷3.8 =4.18÷3.8 =1.1