《2025年课时提优计划作业本七年级数学上册苏科版》

13.(20分)计算：
(1)$(-3\frac{1}{5})× (-\frac{2}{7})÷ (+1\frac{3}{5})$；
(2)$(-\frac{9}{16})÷ (-\frac{3}{8})÷ (-\frac{3}{2})$；
(3)$(-81)× (-\frac{4}{9})÷ \frac{9}{4}× \frac{1}{8}$；
(4)$(-2)÷ (-\frac{3}{7})× \frac{4}{7}÷ (-5\frac{1}{7})$.

答案：
(1)原式$=\frac{16}{5}×\frac{2}{7}×\frac{5}{8}=\frac{4}{7}$.
(2)原式$=-\frac{9}{16}×\frac{8}{3}×\frac{2}{3}=-1$.
(3)原式$=81×\frac{4}{9}×\frac{4}{9}×\frac{1}{8}=2$.
(4)原式$=-2×\frac{7}{3}×\frac{4}{7}×\frac{7}{36}=-\frac{14}{27}$.

14.(20分)计算：
(1)$(-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}-\frac{1}{5})× (-20)$；
(2)$-\frac{5}{6}× (12-2\frac{2}{5}-0.6)$；
(3)$49\frac{24}{25}× (-5)$；
(4)$(-36\frac{4}{5})× \frac{1}{6}$；
(5)$-13× \frac{2}{3}-0.34× \frac{2}{7}+\frac{1}{3}× (-13)-\frac{5}{7}× 0.34$.

答案：
(1)原式$=-\frac{1}{2}×(-20)+\frac{1}{3}×(-20)-\frac{1}{4}×(-20)-\frac{1}{5}×(-20)=10-\frac{20}{3}+5+4=19-\frac{20}{3}=\frac{37}{3}$.
(2)原式$=(-\frac{5}{6})×12-\frac{12}{5}×(-\frac{5}{6})-\frac{3}{5}×(-\frac{5}{6})=-10+2+\frac{1}{2}=-10+2\frac{1}{2}=-7\frac{1}{2}$.
(3)原式$=(50-\frac{1}{25})×(-5)=-(250-\frac{1}{5})=-249\frac{4}{5}$.
(4)原式$=(-36-\frac{4}{5})×\frac{1}{6}=-36×\frac{1}{6}-\frac{4}{5}×\frac{1}{6}=-6-\frac{2}{15}=-6\frac{2}{15}$.
(5)原式$=-13×\frac{2}{3}+\frac{1}{3}×(-13)-0.34×\frac{2}{7}-\frac{5}{7}×0.34=-13×(\frac{2}{3}+\frac{1}{3})-0.34×(\frac{2}{7}+\frac{5}{7})=-13×1-0.34×1=-13-0.34=-13.34$.

15.(12分)根据所学知识回答下列问题.
(1)根据倒数的定义我们知道,若$(a+b)÷ c= 3$,则$c÷ (a+b)=$$\frac{1}{3}$.
(2)计算：$(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})÷ (-\frac{1}{36})$.
$(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})÷(-\frac{1}{36})=(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})×(-36)=-\frac{2}{9}×(-36)+\frac{1}{4}×(-36)-\frac{5}{12}×(-36)=8-9+15=14$.
(3)根据以上信息可知$(-\frac{1}{36})÷ (-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})=$$\frac{1}{14}$.

答案：
(1)$\frac{1}{3}$
(2)$(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})÷(-\frac{1}{36})=(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})×(-36)=-\frac{2}{9}×(-36)+\frac{1}{4}×(-36)-\frac{5}{12}×(-36)=8-9+15=14$.
(3)$\frac{1}{14}$ 解析:由
(2)可知,$(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})÷(-\frac{1}{36})=14$,所以$(-\frac{1}{36})÷(-\frac{2}{9}+\frac{1}{4}-\frac{5}{12})=\frac{1}{14}$.