第12页 - 启东中学作业本七年级数学人教版

$=-7+21-27-5$

$=-18$

$=18-12-21+12$

$=(18-21)+(12-12)$

$=-3$

$=0.35-0.6+0.25-5.4$

$=(0.35+0.25)-(0.6+5.4)$

$=0.6-6$

$=-5.4$

$=-20+14-18-13$

$=-37$

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

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

$=1-4$

$=-3$

$=5.7-8.4-4.2+10$

$=3.1$

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

$=(1 \frac {1}{3}+\frac {5}{3})+(\frac {3}{5}+3 \frac {3}{5}-1 \frac {1}{5})$

$=3+3$

$=6$

$=\frac {2}{5}-\frac {3}{2}-2 \frac {1}{4}+2 \frac {3}{4}$

$=\frac {2}{5}-\frac {3}{2}+\frac {1}{2}$

$=-\frac {3}{5}$

$=1-\frac {1}{2}+\frac {1}{2}-\frac {1}{3}+\frac {1}{3}-\frac {1}{4}+···+\frac {1}{99}-\frac {1}{100}$

$=1-\frac {1}{100}$

$=\frac {99}{100}$