《2024年基础训练大象出版社七年级数学上册人教版》

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

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.