原式=2.9*0.45+2.9*0.42+2.9*0.13
=2.9*（0.45+0.42+0.13）
=2.9*1
=2.9
2.9 ×0.45+0.29 ×4.2+0.029 × 13 =2.9 × 0.45+2.9 × 0.42+2.9 × 0.13 =2.9 × （0.45+0.42+0.13）=2.9
2.9×0.45+0.29×4.2+0.029×13
=0.29×（4.5+4.2+1.3）
=0.29×10
=2.9
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