第45页 - 初中数学课课练七年级苏科版

$ 解：原式(－36)×(\frac {1}{4}－\frac {5}{9}+\frac {1}{12})$

$=(－9)+20－3$

$=8$

$ \begin{aligned} 解：原式&=25×\frac {3}{4}+25×\frac {1}{2}+25×(－\frac {1}{4}) \\ &=25×(\frac {3}{4}+\frac {1}{2}－\frac {1}{4}) \\ &=25×1 \\ &=25 \\ \end{aligned}$

$ $

$ 解：(\frac {1}{6}－\frac {2}{7}+\frac {2}{3}－\frac {3}{14})÷(－\frac {1}{42})$

$=(\frac {1}{6}－\frac {2}{7}+\frac {2}{3}－\frac {3}{14})×(－42)$

$=(－7)+12－28+9$

$=－14所以(－\frac {1}{42})÷(\frac {1}{6}－\frac {2}{7}+\frac {2}{3}－\frac {3}{14})=－\frac {1}{14}$

B

D

－2