分析,根据规律,负负得正,负正得负,正负得负
1,
(-25)-(-18)-(+5)-(+12)
=-25+18-5-12
=-7-17
=-24
2,
-3/5+4/5-1/5-3/2+7/4
=1/5-1/5-3/2+7/4
=7/4-3/2
=(7-6)/4
=1/4