计算下面各题,能简算的要简算.
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| (1)12.7+12.5+0.5 =12.7+(12.5+0.5) =12.7+13 =25.7 (2)2.5×4.6×0.4 =2.5×0.4×4.6 =1×4.6 =4.6 (3)5.4×99+5.4 =5.4×(99+1) =5.4×100 =540 (4)(0.5+0.25)×4 =0.5×4+0.25×4 =2+1 =3 (5)39÷0.125÷8 =39÷(0.125×8) =39÷1 =39 (6)46.5×99+46.5 =46.5×(99+1) =46.5×100 =4650 (7)4.85×1.25×8 =4.85×(1.25×8) =4.85×10 =48.5 (8)(455-12.5×4)÷8.1 =(455-50)÷8.1 =405÷8.1 =50 |
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后,新数比原数少138.6,原数是多少?