1-0.12+1/2-0.34+1/3-0.56+1/5-0.78=（1+1/2+1/3+1/5）-（0.12+0.34+0.56+0.78）
=（30+15+10+6）/30-【（0.12+0.78）+（0.34+0.56）】=61/30-（0.9+0.9）=61/30-1.8=7/30