3.8-8.7×0.3+6.2-6.39=3.8-2.61+6.2-6.39=（3.8+6.2）-（2.61+6.39）=10-9=1
3.8一8.7×0.3+6.2一6.39=3.8一2.61+6.2一6.39=（3.8+6.2）一（2.61+6.39）=10一10=0
