8.34+1.57-3.4=(8.4-0.06)+1.57-3.4=(8.4-3.4)+(1.57-0.06)=5+1.51=6.51
8.34+1.57-3.4=8.34+1.56+0.01-3.4=9.9-3.4+0.01=6.5+0.01=6.51
8.34一3.4十1.57=8+1.57=9.57
