1乘3分之1加3乘5分之1加5乘7分之1加7乘9分之1加……加97乘99分之1 =[(1-1/3)+(1/3-1/5)+(1/5-1/7)+……+(1/97-1/99)]*(1/2)=(1-1/99)*(1/2)=49/99.
