小学六年级难的奥数题简便运算及答案，急用

1/1*3+1/2*4+1/3*5+1/4*6+1/5*7......1/98*100+1/99*101 =（1-1/3+1/2-1/4+1/3-1/5+1/4-1/6+1/5-1/7+……+1/98-1/100+1/99-1/101）÷2 =（1+1/2-1/100-1/101）÷2 =15049/10100