2/1*2*3+2/2*3*4+2/3*4*5+.+2/98*99*100
=1/1×2-1/2×3+1/2×3-1/3×4+……+1/98×99-1/99×100
=1/1×2-1/99×100
=1/2-1/9900
=4949/9900