1/8+1/24+1/80+1/120
=1/8+1/24+1/48+1/80+1/120-1/48
=1/2(1/2-1/4)+1/2(1/4-1/6)+1/2(1/6-1/8)+1/2(1/8-1/10)+1/2(1/10-1/12)-1/48
=1/2(1/2-1/12)-1/48
=3/16
解析:
原式=(1/240)*(30+10+3+2)=(1/240)*45=45/240=3/16
1/8+1/24+1/80+1/120
=(1/8+1/80)+(1/24+1/120)
=11/80+1/20
=15/80
=3/16