Question

15．用簡便方法計(jì)算．
125×$3\frac{1}{5}$×2.5；                $6\frac{1}{4}$×0.125+$\frac{1}{8}$×$2\frac{3}{4}$+12.5%．

Answer 1

分析 ①125×$3\frac{1}{5}$×2.5首先把3$\frac{1}{5}$化成3.2，再把3.2拆分為8×0.4，然后應(yīng)用乘法結(jié)合律簡便；
②$6\frac{1}{4}$×0.125+$\frac{1}{8}$×$2\frac{3}{4}$+12.5%，首先把分?jǐn)?shù)百分?jǐn)?shù)化成小數(shù)，將原式轉(zhuǎn)化為：6.25×0.125+0.125×2.75+0.125，再運(yùn)用乘法分配律簡算．

解答 解：①125×$3\frac{1}{5}$×2.5
=125×3.2×2.5
=（125×8）×（0.4×2.5）
=1000×1
=1000；

②$6\frac{1}{4}$×0.125+$\frac{1}{8}$×$2\frac{3}{4}$+12.5%
=6.25×0.125+0.125×2.75+0.125
=（6.25+2.75+1）×0.125
=10×0.125
=1.25．

點(diǎn)評 此題考查的目的是理解掌握整數(shù)、分?jǐn)?shù)、小數(shù)四則混合運(yùn)算的順序以及它們的計(jì)算法則，并且能夠靈活運(yùn)用乘法的運(yùn)算定律進(jìn)行簡便計(jì)算．