1/2 +1/(2+4) +1/(2+4+6) +1/(2+4+6+8)+…….+1/(2+4+6+8+…….+100) =1/（1×2 ）+1/(2×3) +1/(3×4) +1/(4×5)+…….+1/(50×51) =1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+….+1/50-1/51 =1-1/51 =50/51