1999*0.5分之1997*0.3+1999分之1.2(1)1/2+5/6+11/12+19/20+29/30+41/42(2)(224+1/222)*1/223,要精确，

1999*0.5分之1997*0.3+1999分之1.2=（1997*0.3）/（1999*0.5）+1.2/1999=（1999*0.3-2*0.3）/（1999*0.5）+1.2/1999=3/5-（6/5）/1999+1.2/1999=
3/5-1.2/1999+1.2/1999=3/5
靠，刚发就补充了
1.1/2+5/6+11/12+19/20+29/30+41/42=6-1/2-1/6-1/12-1/20-1/30-1/42
=6-【（1-1/2）+（1/2-1/3）+（1/3-1/4）+（1/4-1/5）+（1/5-1/6）+（1/6-1/7）】=6-（1-1/7）=36/7
2.（224+1/222)*1/223=（223+223/222）*1/223=1+1/222=224/223

(1997*0.3)/(1999*0.5)+1.2/1999
=(1997*0.6)/(1999*1)+1.2/1999
=(1997*0.6+1.2)/1999
=[(1999-2)*0.6+1.2]/1999
=(1999*0.6-1.2+1.2)/1999
=0.6
1/2+5/6+11/12+19/20+29/30+41/42
=(1-1/2)+(1-1/6)+(1-1/12)+(1-1/20)+(1-1/30)+(1-1/42)
=6-(1/2+1/6+1/12+1/20+1/30+1/42)
=6-(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=6-(1-1/7)
=6-6/7
=5又1/7
(224+1/222)*1/223
=(223+223/222)*1/223
=1+1/223
=224/223