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12.8×0.75+2.5×1.28簡便運算

12.8×0.75+2.5×1.28簡便運算

12.8×0.75+2.5×1.28
=1.28×7.5+1.26×2.5
=1.28×（7.5+2.5）
=1.28×10
=12.8

4×0.8×12.5×0.2簡便運算

4×0.8×12.5×0.2
=4×（0.8×12.5）×0.2
=4×（10×0.2）
=4×2
=8
題目主要運用的是乘法交換律，交換之後運算方便多了

-4+（-12）+0.5+8+（-1/2）簡便運算

=-（4+12）+（0.5-1/2）+8
=-16+0+8
=8