《2025年基础训练大象出版社七年级数学上册人教版》

2. (★★)计算：
(1) $\frac {1}{4}+(-\frac {2}{3})+\frac {5}{6}+(-\frac {1}{4})+(-\frac {1}{3})$；
(2) $3.587-(-5)+(-5\frac {1}{2})+(+7)-(+3\frac {1}{4})-(+1.587)$；
(3) $-0.125×7×(-5)×8$；
(4) $(-60)×(\frac {3}{4}+\frac {5}{6}-\frac {11}{15})$；
(5) $49\frac {24}{25}×(-5)$；
(6) $(-\frac {1}{12}+\frac {1}{3}-\frac {1}{2})÷(-\frac {1}{18})$；
(7) $25×\frac {3}{4}-(-25)×\frac {1}{2}+25×(-\frac {1}{4})$；
(8) $-13×\frac {2}{3}-0.34×\frac {2}{7}+\frac {1}{3}×(-13)-\frac {5}{7}×0.34$。

答案： 解:
(1)原 式$ = [\frac{1}{4}+(-\frac{1}{4})]+[(-\frac{2}{3})+(-\frac{1}{3})]+\frac{5}{6}$
$=-1+\frac{5}{6}$
$=-\frac{1}{6}$
解:
(2)原式$=3.587+5+(-5\frac{1}{2})+(+7)+ (-3\frac{1}{4})+(-1.587)\ $
$=[3.587+(-1.587)]+(5+7)+[(-5\frac{1}{2})+(-3\frac{1}{4})]\ $
$=2+12+(-8\frac{3}{4})$
$=5\frac{1}{4}.$
解:
(3)原式=0.125×8×7×5
=35.
解:
(4)原式$=-60×\frac{3}{4}-60×\frac{5}{6}+60×\frac{11}{15}\ $
=-45-50+44
=-51.
解:
(5)原式$=(50-\frac{1}{25})×(-5)\ $
$=-250+\frac{1}{5}\ $
$=-249\frac{4}{5}$
解:
(6)原式$=(-\frac{1}{12} +\frac{1}{3}-\frac{1}{2})×(-18)$
=4.5
解:
(7)原式$=25×(\frac{3}{4}-\frac{1}{4}+\frac{1}{2})$
$=25×(\frac {1}{2}+\frac {1}{2})$
=25.
原式$=(-13)×(\frac {2}{3}+\frac {1}{3})+(\frac {5}{7}+\frac {2}{7})×(-0.34)$
=-13-0.34
=-13.34.