Question

14．怎樣簡便就怎樣算．
$\frac{3}{5}×\frac{3}{4}+\frac{2}{5}×\frac{3}{4}$          
（$\frac{1}{2}$-$\frac{1}{3}$+$\frac{1}{4}$）×48           
49×$\frac{3}{48}$．

Answer 1

分析 ①$\frac{3}{5}×\frac{3}{4}+\frac{2}{5}×\frac{3}{4}$，運用乘法分配律簡算；
②（$\frac{1}{2}$-$\frac{1}{3}$+$\frac{1}{4}$）×48，運用乘法分配律簡算；      
③49×$\frac{3}{48}$，轉(zhuǎn)化為：（48+1）×$\frac{3}{48}$，運用乘法分配律簡算．

解答 解：①$\frac{3}{5}×\frac{3}{4}+\frac{2}{5}×\frac{3}{4}$
=$（\frac{3}{5}+\frac{2}{5}）×\frac{3}{4}$
=$1×\frac{3}{4}$
=$\frac{3}{4}$；

②（$\frac{1}{2}$-$\frac{1}{3}$+$\frac{1}{4}$）×48   
=$\frac{1}{2}×48-\frac{1}{3}×48+\frac{1}{4}×48$
=24-16+12
=8+12
=20；
        
③49×$\frac{3}{48}$
=（48+1）×$\frac{3}{48}$
=$48×\frac{3}{48}+1×\frac{3}{48}$
=$3+\frac{3}{48}$
=$3\frac{3}{48}$．

點評 此題考查的目的是理解掌握乘法分配律的意義及應(yīng)用．