将8.24拆成5.24和3，先用3减去2.96得到0.04，再用0.04加上5.24得到结果5.28。
8.24-2.96=824/100-296/100=（800+24-200-96）/100=538/100=5.38
8.24一2.96=8.24一3十0.04=5.28
8.24-2.96=8.24-3+0.04=5.24+0.04=5.28
