1 直接写出得数。
$ \frac{5}{6} × 15 = $
$ 1 ÷ 50\% = $
$ \frac{5}{39} × \frac{13}{15} = $
$ \frac{5}{6} × 15 = $
$\frac{25}{2}$
$ \frac{2}{3} ÷ \frac{4}{9} = $$\frac{3}{2}$
$ 1 ÷ 50\% = $
2
$ 2 - \frac{7}{10} = $$\frac{13}{10}$
$ \frac{5}{39} × \frac{13}{15} = $
$\frac{1}{9}$
$ \frac{1}{9} - \frac{1}{9} × \frac{1}{9} = $$\frac{8}{81}$
答案：$\frac{25}{2}$；$\frac{3}{2}$；2；$\frac{13}{10}$；$\frac{1}{9}$；$\frac{8}{81}$
2 计算下面各题。
$ \frac{3}{5} × \frac{5}{27} × \frac{3}{8} \frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9} $
$ \frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4} \frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2} $
$ \frac{3}{5} × \frac{5}{27} × \frac{3}{8} \frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9} $
$ \frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4} \frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2} $
答案：
1. $\frac{1}{24}$
2. $\frac{3}{4}$
3. $\frac{9}{10}$
4. $\frac{1}{15}$
1. $\frac{1}{24}$
2. $\frac{3}{4}$
3. $\frac{9}{10}$
4. $\frac{1}{15}$
解析：
第一题：$\frac{3}{5} × \frac{5}{27} × \frac{3}{8}$
$\begin{aligned}&\frac{3}{5} × \frac{5}{27} × \frac{3}{8}\\=&\frac{3×5×3}{5×27×8}\\=&\frac{45}{1080}\\=&\frac{1}{24}\end{aligned}$
第二题：$\frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9}$
$\begin{aligned}&\frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9}\\=&\frac{2}{3} × \frac{5}{4} × \frac{9}{10}\\=&\frac{2×5×9}{3×4×10}\\=&\frac{90}{120}\\=&\frac{3}{4}\end{aligned}$
第三题：$\frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4}$
$\begin{aligned}&\frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4}\\=&\frac{8}{15} × \frac{9}{4} × \frac{3}{4}\\=&\frac{8×9×3}{15×4×4}\\=&\frac{216}{240}\\=&\frac{9}{10}\end{aligned}$
第四题：$\frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2}$
$\begin{aligned}&\frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2}\\=&\frac{11}{16} × \frac{8}{5} × \frac{2}{33}\\=&\frac{11×8×2}{16×5×33}\\=&\frac{176}{2640}\\=&\frac{1}{15}\end{aligned}$
$\begin{aligned}&\frac{3}{5} × \frac{5}{27} × \frac{3}{8}\\=&\frac{3×5×3}{5×27×8}\\=&\frac{45}{1080}\\=&\frac{1}{24}\end{aligned}$
第二题：$\frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9}$
$\begin{aligned}&\frac{2}{3} × \frac{5}{4} ÷ \frac{10}{9}\\=&\frac{2}{3} × \frac{5}{4} × \frac{9}{10}\\=&\frac{2×5×9}{3×4×10}\\=&\frac{90}{120}\\=&\frac{3}{4}\end{aligned}$
第三题：$\frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4}$
$\begin{aligned}&\frac{8}{15} ÷ \frac{4}{9} × \frac{3}{4}\\=&\frac{8}{15} × \frac{9}{4} × \frac{3}{4}\\=&\frac{8×9×3}{15×4×4}\\=&\frac{216}{240}\\=&\frac{9}{10}\end{aligned}$
第四题：$\frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2}$
$\begin{aligned}&\frac{11}{16} ÷ \frac{5}{8} ÷ \frac{33}{2}\\=&\frac{11}{16} × \frac{8}{5} × \frac{2}{33}\\=&\frac{11×8×2}{16×5×33}\\=&\frac{176}{2640}\\=&\frac{1}{15}\end{aligned}$
1 计算下面各题,怎样算简便就怎样算。
$ \frac{8}{15} - (\frac{2}{15} + \frac{2}{5}) \frac{3}{5} × \frac{19}{25} + \frac{3}{5} × \frac{6}{25} $
$ (\frac{7}{10} + \frac{2}{5}) × (\frac{3}{2} - \frac{2}{3}) \frac{3}{20} ÷ [\frac{1}{3} × (\frac{2}{5} + \frac{4}{5})] $
$ \frac{8}{15} - (\frac{2}{15} + \frac{2}{5}) \frac{3}{5} × \frac{19}{25} + \frac{3}{5} × \frac{6}{25} $
$ (\frac{7}{10} + \frac{2}{5}) × (\frac{3}{2} - \frac{2}{3}) \frac{3}{20} ÷ [\frac{1}{3} × (\frac{2}{5} + \frac{4}{5})] $
答案：1.
$\frac{8}{15}-(\frac{2}{15}+\frac{2}{5})$
$=\frac{8}{15} - (\frac{2}{15}+\frac{6}{15})$
$=\frac{8}{15}-\frac{8}{15}$
$=0$
2.
$\frac{3}{5}×\frac{19}{25}+\frac{3}{5}×\frac{6}{25}$
$=\frac{3}{5}×(\frac{19}{25}+\frac{6}{25})$
$=\frac{3}{5}×1$
$=\frac{3}{5}$
3.
$(\frac{7}{10}+\frac{2}{5})×(\frac{3}{2}-\frac{2}{3})$
$=(\frac{7}{10}+\frac{4}{10})×(\frac{9}{6}-\frac{4}{6})$
$=\frac{11}{10}×\frac{5}{6}$
$=\frac{11}{12}$
4.
$\frac{3}{20}÷[\frac{1}{3}×(\frac{2}{5}+\frac{4}{5})]$
$=\frac{3}{20}÷[\frac{1}{3}×\frac{6}{5}]$
$=\frac{3}{20}÷\frac{2}{5}$
$=\frac{3}{20}×\frac{5}{2}$
$=\frac{3}{8}$
$\frac{8}{15}-(\frac{2}{15}+\frac{2}{5})$
$=\frac{8}{15} - (\frac{2}{15}+\frac{6}{15})$
$=\frac{8}{15}-\frac{8}{15}$
$=0$
2.
$\frac{3}{5}×\frac{19}{25}+\frac{3}{5}×\frac{6}{25}$
$=\frac{3}{5}×(\frac{19}{25}+\frac{6}{25})$
$=\frac{3}{5}×1$
$=\frac{3}{5}$
3.
$(\frac{7}{10}+\frac{2}{5})×(\frac{3}{2}-\frac{2}{3})$
$=(\frac{7}{10}+\frac{4}{10})×(\frac{9}{6}-\frac{4}{6})$
$=\frac{11}{10}×\frac{5}{6}$
$=\frac{11}{12}$
4.
$\frac{3}{20}÷[\frac{1}{3}×(\frac{2}{5}+\frac{4}{5})]$
$=\frac{3}{20}÷[\frac{1}{3}×\frac{6}{5}]$
$=\frac{3}{20}÷\frac{2}{5}$
$=\frac{3}{20}×\frac{5}{2}$
$=\frac{3}{8}$
$2 $在下面的长方形里涂上颜色$,$表示$ \frac{1}{2} × \frac{1}{3} $的意义。
答案：
2
2
3 “十一”期间,五星商场搞促销活动。一种彩电原价 2800 元,现价比原价降低了 700 元。这种彩电单价降低了百分之几？
答案：3 25%
解析：
$700÷2800$
$=0.25$
$=25\%$
答：这种彩电单价降低了$25\%$。
$=0.25$
$=25\%$
答：这种彩电单价降低了$25\%$。