Question

13．计算下面各题
①3×$\frac{2}{7}$×$\frac{5}{21}$       
②$\frac{3}{5}$×$\frac{3}{4}$+$\frac{2}{5}$×$\frac{3}{4}$
③24×（$\frac{1}{8}$+$\frac{1}{6}$）        
④（$\frac{1}{3}$+$\frac{1}{4}$$-\frac{1}{24}$）×24．

Answer 1

分析 ①从左向右依次计算即可．
②③④根据乘法分配律简算即可．

解答 解：①3×$\frac{2}{7}$×$\frac{5}{21}$    
=$\frac{6}{7}$×$\frac{5}{21}$  
=$\frac{10}{49}$

②$\frac{3}{5}$×$\frac{3}{4}$+$\frac{2}{5}$×$\frac{3}{4}$
=（$\frac{3}{5}$+$\frac{2}{5}$）×$\frac{3}{4}$
=1×$\frac{3}{4}$
=$\frac{3}{4}$

③24×（$\frac{1}{8}$+$\frac{1}{6}$）        
=24×$\frac{1}{8}$+24×$\frac{1}{6}$
=3+4
=7

④（$\frac{1}{3}$+$\frac{1}{4}$$-\frac{1}{24}$）×24
=$\frac{1}{3}$×24+$\frac{1}{4}$×24$-\frac{1}{24}$×24
=8+6-1
=13

点评 此题主要考查了分数四则混合运算，注意运算顺序，注意乘法运算定律的应用．