四年级速算与巧算数学思维练习题（十八）(2)
网络资源
2018-03-01 17:59:52
1/2+1/6+1/12+1/20+1/30+.+1/9900
=1/1×2+1/2×3+1/3×4+1/4×5+1/5×6+.+1/99×100
=（1-1/2）+（1/2-1/3）+（1/3-1/4）+（1/4-1/5）+（1/5-1/6）+.+1/99-1/100
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+.+1/99-1/100
=1-1/100
=99/100
