Question

16．能簡算的要簡算．

17×$\frac{9}{16}$	（ $\frac{3}{4}$+$\frac{5}{8}$）×8×4	$\frac{5}{9}$-$\frac{5}{9}$×$\frac{3}{4}$
$\frac{5}{4}$×$\frac{1}{8}$×16	$\frac{1}{5}$+$\frac{2}{9}$×$\frac{3}{10}$	（ $\frac{5}{6}$+$\frac{2}{3}$-$\frac{7}{12}$）×48

Answer 1

分析 ①把17變成16+1，再用乘法分配律計(jì)算．
②用乘法分配律計(jì)算．a(chǎn)×（b+c）=ab+ac．
③用乘法分配律計(jì)算．
④先乘后兩個(gè)數(shù)，再和第一個(gè)數(shù)相乘．
⑤先算乘法，再算加法．
⑥用乘法分配律計(jì)算．

解答 解：①17×$\frac{9}{16}$    
=（16+1）×$\frac{9}{16}$ 
=16×$\frac{9}{16}$+1×$\frac{9}{16}$
=9+$\frac{9}{16}$
=$9\frac{9}{16}$
    
②（ $\frac{3}{4}$+$\frac{5}{8}$）×8×4     
=$\frac{3}{4}$×8×4+$\frac{5}{8}$×8×4
=24+20
=44
     
③$\frac{5}{9}-\frac{5}{9}×\frac{3}{4}$
=$（1-\frac{3}{4}）×\frac{5}{9}$
=$\frac{1}{4}×\frac{5}{9}$
=$\frac{5}{36}$

④$\frac{5}{4}×\frac{1}{8}×16$
=$\frac{5}{4}×（\frac{1}{8}×16）$
=$\frac{5}{4}×2$
=$\frac{5}{2}$

⑤$\frac{1}{5}$+$\frac{2}{9}$×$\frac{3}{10}$ 
=$\frac{1}{5}+\frac{1}{15}$
=$\frac{3}{15}+\frac{1}{15}$
=$\frac{4}{15}$

⑥（ $\frac{5}{6}$+$\frac{2}{3}$-$\frac{7}{12}$）×48
=48×$\frac{5}{6}$+$\frac{2}{3}$×48-$\frac{7}{12}$×48
=40+32-28
=72-28
=44

點(diǎn)評 脫式計(jì)算要觀察算式的特點(diǎn)，靈活選用簡便方法計(jì)算．