能用简便方法计算的要用简便方法计算.
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| ①0.8×(12.5+1.25) =0.8×12.5+0.8×1.25 =10×1 =10; ②2.5+7.5×(8.65-2.25) =2.5+7.5×6.4 =2.5+48 =50.5; ③2.5×0.4÷2.5×0.4 =2.5÷2.5×0.4×0.4 =1×0.4×0.4 =0.16; ④2.5×2.8×2 =2.8×(2.5×2) =2.8×5 =14; ⑤24.59-1.05+4.41-6.95 =24.59+4.41-(1.05+6.95) =29-8 =21. |
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a.缩小为原来的[ ]
[ ]
a.4.5÷l.5
,那么积[ ]
a.扩大为原来的5倍
,另一个因数不变,积[ ]
a.扩大为原来的100倍