【正确答案】①7.9936÷0.9967-5.02=7.994÷0.9967-5.02
   =8.020-5.02=8.02-5.02=3.00
   ② 0.414÷(31.3×0.05307)=0.414÷(31.3×0.0531)
   =0.414÷1.66=0.249
   ③(1.276×4.17)+1.7×10^-4-(0.0021764×0.0121)
   =(1.28×4.17)+1.7×10^-4-(0.00218×0.0121)
   =5.34+1-7×10^-4-0.0000264≈5.34