0.37X7.9=0.37✘（8-0.1）=0.37✘8-0.37✘0.1=2.96-0.037=2.923 3.7✘0.21=3.7✘（0.2+0.01）=3.7✘0.2+3.7✘0.01=7.4+0.037=7.437
