12.09÷2+1.91×0.5=(12.09+1.91)/2=7
6.5×8+3.5×8+4.4=(13+7+1.1)*4=84.4
9-20/13-20/7你确定是20/13,20/7不是13/20,7/20?
5/2×8+5/3×8+8同上,确定没写反?
3.15-(0.16+1.15)-1.84=(3.15-1.15)-(0.16+1.84)=0
0.8÷[1÷(3.2-2.95)]=0.8*0.25=0.2
(7/5÷1)÷(1÷7/5)=7/5*7/5=49/25
6÷[8.9+(10-8.9)]=6/10=0.6