Question

5．用簡(jiǎn)便方法計(jì)算．
$\frac{1}{4}$×32+0.25×68；      
$\frac{2}{9}$+（$\frac{7}{9}$-$\frac{2}{5}$）-$\frac{3}{5}$；      
$\frac{9}{5}$×2.5×$\frac{5}{9}$×0.04．

Answer 1

分析 （1）把$\frac{1}{4}$化成0.25，用乘法分配律計(jì)算．a(chǎn)×c+b×c=（a+b）×c．
（2）根據(jù)加法的性質(zhì)，把括號(hào)直接去掉，先算$\frac{2}{9}+\frac{7}{9}$得1，再根據(jù)減法的性質(zhì)用1減去$\frac{2}{5}$和$\frac{3}{5}$的和．
（3）根據(jù)乘法交換律和乘法結(jié)合律，先算$\frac{9}{5}×\frac{5}{9}$得1，再算2.5×0.04得0.1，最后用1乘0.1即可．

解答 （1）$\frac{1}{4}$×32+0.25×68
=0.25×（32+68）
=0.25×100
=25

（2）$\frac{2}{9}$+（$\frac{7}{9}$-$\frac{2}{5}$）-$\frac{3}{5}$
=$\frac{2}{9}$+$\frac{7}{9}$-$\frac{2}{5}$-$\frac{3}{5}$
=1-（$\frac{2}{5}$+$\frac{3}{5}$）
=1-1
=0

（3）$\frac{9}{5}$×2.5×$\frac{5}{9}$×0.04
=（$\frac{9}{5}$×$\frac{5}{9}$）（2.5×0.04）
=1×0.1
=0.1

點(diǎn)評(píng) 考查了根據(jù)算式的特點(diǎn)靈活運(yùn)用簡(jiǎn)便方法計(jì)算算式．