Question

13．怎样简便就怎样算．
$\frac{4}{9}$×$\frac{1}{5}$÷$\frac{4}{5}$                  
36×（$\frac{2}{3}$+$\frac{1}{6}$-$\frac{3}{4}$）                   
$\frac{1}{8}$×58+42÷8．

Answer 1

分析 ①把除法变乘法，再运用乘法交换律结合律简算；
②运用乘法的分配律简算；
③把除法变乘法，再运用乘法分配律简算．

解答 解：①$\frac{4}{9}$×$\frac{1}{5}$÷$\frac{4}{5}$       
=$\frac{4}{9}$×$\frac{1}{5}$×$\frac{5}{4}$
=$\frac{4}{9}$×$\frac{1}{4}$
=$\frac{1}{9}$

           
②36×（$\frac{2}{3}$+$\frac{1}{6}$-$\frac{3}{4}$）            
=36×$\frac{2}{3}$+36×$\frac{1}{6}$-36×$\frac{3}{4}$
=24+6-27
=30-27
=3

       
③$\frac{1}{8}$×58+42÷8
=$\frac{1}{8}$×58+42×$\frac{1}{8}$
=$\frac{1}{8}$×（58+42）
=$\frac{1}{8}$×100
=$\frac{25}{2}$

点评 完成本题要注意分析式中数据，运用合适的简便方法计算．