1/3+1/6+1/10+……+1/4950=1/2×（1/6+1/12+1/20+……+1/9900）=1/2×（1/2-1/3+1/3-1/4+1/4-1/5+……+1/99-1/100）=1/2×（1/2-1/100）=1/2×49/100=49/200
