1. 2又6209/10013*10693/22869÷33337/106022. (1/2-1/3)+(1/4-1/5)+(1/7-1/10)+(1/14-1/15)+(1/28-1/30)3. 1/(1*2)+1/(2*3)+1/(3*4)+...+1/(999*1000)4. 1+1/(1*2)+1/(1+2+3)+...+1/(1+2+3+...+20)5. 1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+...+1/(98*99*100)