第10页 - 江苏版启东中学作业本七年级数学（上下册）

$=-8+15-9+12$

$=-(8+9)+(15+12)$

$=-17+27$

$=10$

$=-12-5-14+39$

$=8$

$=6.2-4.6+3.6+2.8$

$=(6.2+2.8)-(4.6-3.6)$

$=9-1$

$=8$

=2+2-3+3

=4

$=\frac {1}{4}-\frac {1}{8}-\frac {3}{4}-\frac {7}{8}$

$=-(\frac {3}{4}-\frac {1}{4})-(\frac {1}{8}+\frac {7}{8})$

$=-\frac {1}{2}-1$

$=-1.5$

$=\frac {5}{6}-2 \frac {1}{2}+1 \frac {1}{6}-\frac {1}{2}$

$=(\frac {5}{6}+1 \frac {1}{6})-(2 \frac {1}{2}+\frac {1}{2})$

$=2-3$

$=-1$

$=5 \frac {3}{4}+4 \frac {2}{3}-5 \frac {3}{4}-7 \frac {2}{3}$

$=(5 \frac {3}{4}-5 \frac {3}{4})-(7 \frac {2}{3}-4 \frac {2}{3})$

$=0-3$

$=-3$

$=-\frac {31}{3}+\frac {58}{7}-\frac {9}{7}-\frac {32}{3}$

$=-(\frac {31}{3}+\frac {32}{3})+(\frac {58}{7}-\frac {9}{7})$

$=-21+7$

$=-14$

$=-4 \frac {7}{9}+3 \frac {1}{6}-\frac {2}{9}+6 \frac {1}{6}$

$=-(4 \frac {7}{9}+\frac {2}{9})+(3 \frac {1}{6}+6 \frac {1}{6})$

$=-5+9 \frac {1}{3}$

$=4\frac {1}{3}$

$=(301-301)+(125-75)$

$=0+50$

$=50$