谁帮我出几道简便运算？五年级小数加减法

34.5×8.23-34.5+2.77×34.5
19.98×37-199.8×1.9+1998×0.82
314×0.043+3.14×7.2-31.4×0.15
3.9×1.2+0.12
75×4.7+15.9×25
7.5×23+31×2.5

答案：34.5×8.23-34.5+2.77×34.5
=34.5*（8.23-1+2.77）
=34.5*10=345

19.98×37-199.8×1.9+1998×0.82
=19.98*37-19.98*19+19.98*82
=19.98*(37-19+82)=19.98*100=1998

314×0.043+3.14×7.2-31.4×0.15
=3.14*4.3+3.14*7.2-3.14*1.5
=3.14*(4.3+7.2-1.5)=3.14*10=31.4

3.9×1.2+0.12
=3.9*1.2+0.1*1.2
=(3.9+0.1)*1.2=4*1.2=4.8

75×4.7+15.9×25
=25*3*4.7+15.9*25
=25*(14.1+15.9)
=25*30=750

7.5×23+31×2.5
=2.5*3*23+31*2.5
=2.5*(69+31)
=2.5*100=250

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