Question

3．能簡算的要簡算．

17×$\frac{9}{16}$	（ $\frac{3}{4}$+$\frac{5}{8}$）×32	$\frac{5}{9}$×$\frac{3}{4}$+$\frac{5}{9}$×$\frac{1}{4}$
$\frac{5}{4}$×$\frac{1}{8}$×16	$\frac{16}{5}×3÷\frac{4}{5}$	$\frac{25}{9}÷\frac{5}{4}÷\frac{4}{5}$．

Answer 1

分析 ①②③運(yùn)用乘法分配律可簡便計(jì)算，
④運(yùn)用乘法結(jié)合律可簡便計(jì)算，
⑤運(yùn)用乘法交換律可簡便計(jì)算，
⑥把除法變成乘法即可簡算．

解答 解：①17×$\frac{9}{16}$
=（16+1）×$\frac{9}{16}$
=16×$\frac{9}{16}$+$\frac{9}{16}$
=9+$\frac{9}{16}$
=$9\frac{9}{16}$

②（$\frac{3}{4}$+$\frac{5}{8}$）×32
=$\frac{3}{4}$×32+$\frac{5}{8}$×32
=24+20
=44

③$\frac{5}{9}$×$\frac{3}{4}$+$\frac{5}{9}$×$\frac{1}{4}$
=$\frac{5}{9}$×（$\frac{3}{4}$+$\frac{1}{4}$）
=$\frac{5}{9}$×1
=$\frac{5}{9}$

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

⑤$\frac{6}{5}$×3÷$\frac{4}{5}$
=$\frac{6}{5}$×3×$\frac{5}{4}$
=$\frac{6}{5}$×$\frac{5}{4}$×3
=$\frac{3}{2}$×3
=$\frac{9}{2}$

⑥$\frac{25}{9}$÷$\frac{5}{4}$÷$\frac{4}{5}$
=$\frac{25}{9}$×$\frac{4}{5}$×$\frac{5}{4}$
=$\frac{25}{9}$

點(diǎn)評(píng) 此題考查分?jǐn)?shù)四則混合運(yùn)算法則和靈活運(yùn)用乘法分配律、結(jié)合律和交換律．