题目应该是这样吧? 1/8+1/24+1/48+1/80=
原式= 1/2( 1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10)=1/2(1/2-1/10)=1/5
1/8+1/24+1/48+1/80+1/120
=1/2*4+1/4*6+1/6*8+1/8*10+1/10*12
=1/2(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)
=1/2*(1/2-1/12)
=1/2*5/12
=5/24
1/8+120/1=1.15/8 3.45/24+1/24+0.5/24=4.95/24=99/480