1乘3乘5分之4加3乘5乘7分之4+...+95乘97乘99分之4
=1/(1×3)-1/(3×5) +1/(3×5)-1/(5×7)+...+1/(95×97)-1/(97×99)
=1/(1×3)-1/(97×99)
=3201/9603-1/9603
=3200/9603