Question

15．計(jì)算下面各題．
$\frac{4}{7}$×$\frac{21}{10}$×$\frac{2}{5}$                
$\frac{3}{5}$×$\frac{2}{9}$×15
4×$\frac{5}{12}$÷$\frac{5}{9}$                 
$\frac{1}{2}$÷$\frac{5}{4}$×$\frac{2}{3}$．

Answer 1

分析 （1）從左往右依次計(jì)算；
（2）運(yùn)用乘法交換律與結(jié)合律簡算；
（3）（4）把除法變?yōu)槌朔�，約分計(jì)算．

解答 解：（1）$\frac{4}{7}$×$\frac{21}{10}$×$\frac{2}{5}$  
=$\frac{6}{5}$×$\frac{2}{5}$  
=$\frac{12}{25}$

（2）$\frac{3}{5}$×$\frac{2}{9}$×15
=（$\frac{3}{5}$×15）×$\frac{2}{9}$
=9×$\frac{2}{9}$
=2

（3）4×$\frac{5}{12}$÷$\frac{5}{9}$ 
=4×$\frac{5}{12}$×$\frac{9}{5}$
=3

（4）$\frac{1}{2}$÷$\frac{5}{4}$×$\frac{2}{3}$
=$\frac{1}{2}$×$\frac{4}{5}$×$\frac{2}{3}$
=$\frac{4}{15}$

點(diǎn)評(píng) 此題考查了分?jǐn)?shù)的四則混合運(yùn)算，注意運(yùn)算順序和運(yùn)算法則，靈活運(yùn)用所學(xué)的運(yùn)算定律簡便計(jì)算．