Question

13．能簡(jiǎn)算的要簡(jiǎn)算．
$\frac{7}{8}$×$\frac{4}{9}$+$\frac{7}{8}$×$\frac{5}{9}$          
$\frac{3}{5}$×4×$\frac{3}{4}$              
$\frac{5}{7}$×16×$\frac{21}{5}$
$\frac{1}{3}$×$\frac{3}{5}$+1       
$\frac{7}{8}$×7+$\frac{3}{8}$              
87×$\frac{3}{86}$．

Answer 1

分析 ①運(yùn)用乘法的分配律簡(jiǎn)算；
②運(yùn)用乘法結(jié)合律簡(jiǎn)算；
③運(yùn)用乘法交換律簡(jiǎn)算；
④、⑤先算乘法再算加法；
⑥先把87分解成86+1，再運(yùn)用乘法分配律簡(jiǎn)算．

解答 解：①$\frac{7}{8}$×$\frac{4}{9}$+$\frac{7}{8}$×$\frac{5}{9}$
=$\frac{7}{8}$×（$\frac{4}{9}$+$\frac{5}{9}$）   
=$\frac{7}{8}$
     
②$\frac{3}{5}$×4×$\frac{3}{4}$   
=$\frac{3}{5}$×（4×$\frac{3}{4}$ ）
=$\frac{3}{5}$×3 
=$\frac{9}{5}$
         
③$\frac{5}{7}$×16×$\frac{21}{5}$
=$\frac{5}{7}$×$\frac{21}{5}$×16
=3×16
=48

④$\frac{1}{3}$×$\frac{3}{5}$+1    
=$\frac{1}{5}$+1
=$\frac{6}{5}$ 

⑤$\frac{7}{8}$×7+$\frac{3}{8}$
=$\frac{49}{8}$+$\frac{3}{8}$
=$\frac{13}{2}$
    
⑥87×$\frac{3}{86}$
=（86+1）×$\frac{3}{86}$
=3$\frac{3}{86}$

點(diǎn)評(píng) 此題是考查分?jǐn)?shù)的四則混合運(yùn)算，要仔細(xì)觀察算式的特點(diǎn)，靈活運(yùn)用一些定律進(jìn)行簡(jiǎn)便計(jì)算．