[其他] 紧急求助五年级奥数题

=10-(1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110)
=10-(1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10+1/10*11)
=10-(1-1/2+1/2-1/3+1/3-1/4+---------+1/10-1/11)
=10-(1-1/11)
=9又1/11.