计算2/1+6/1+12/1……+90/1

Question

计算2/1+6/1+12/1……+90/1

Answer 1

PS:1/6=1/2-1/3
1/12=1/3-1/4
所以1/2+(1/2-1/3)+(1/3-1/4)+.+(1/9-1/10)=1/2-1/10=2/5=0.4