Question

8．計(jì)算下面各題，怎樣算簡(jiǎn)便就怎樣算．
0.25×4.78×4                      
7.6×18+18×2.4
$\frac{3}{4}$×$\frac{1}{7}$+$\frac{1}{4}$÷7              
5÷[（$\frac{2}{3}$+$\frac{1}{5}$）×$\frac{1}{13}$]．

Answer 1

分析 ①根據(jù)乘法交換律及結(jié)合律計(jì)算；
②根據(jù)乘法分配律進(jìn)行計(jì)算；
③$\frac{1}{4}$除以7，等于$\frac{1}{4}$乘$\frac{1}{7}$，再根據(jù)乘法分配律進(jìn)行計(jì)算；
④先算加法，再算乘法，最后算除法．

解答 解：①0.25×4.78×4    
=0.25×4×4.78
=1×4.78
=4.78
                  
②7.6×18+18×2.4
=18×（7.6+2.4）
=18×10
=180

③$\frac{3}{4}$×$\frac{1}{7}$+$\frac{1}{4}$÷7      
=$\frac{3}{4}$×$\frac{1}{7}$+$\frac{1}{4}$×$\frac{1}{7}$
=$\frac{1}{7}$×（$\frac{3}{4}$+$\frac{1}{4}$）
=$\frac{1}{7}$×1
=$\frac{1}{7}$
        
④5÷[（$\frac{2}{3}$+$\frac{1}{5}$）×$\frac{1}{13}$]
=5÷[$\frac{13}{15}$×$\frac{1}{13}$]
=5÷$\frac{1}{15}$
=75

點(diǎn)評(píng) 完成本題要注意分析式中數(shù)據(jù)，運(yùn)用合適的簡(jiǎn)便方法計(jì)算．