用裂项法解：1/3+1/15+1/35+1/63+1/99

=1/2(1-1/3)+1/2(1/3-1/5)+1/2(1/5-1/7)+1/2(7/1-1/9)+1/2(1/9-1/11)
=1/2(1-1/11)
=5/11
手机提问的朋友在客户端右上角评价点【满意】即可.
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