1、原式=61*(1-1/60)+(121+121/120)/11
=61-61/60+11+11/120
=61-1-2/120+11+11/120
=71+3/40
=71又40分之3
2、原式=1/4-1/5+1/5-1/6+……+1/39-1/40
=1/4-1/40
=10/40-1/40
=9/40
裂项就可以了
3、原式=0.1111×（9×0.7+2.7）
=0.1111×（6.3+2.7）
=0.1111×9
=0.9999