1/3+1/8+1/15+.+1/120

　　=1/(1*3)+1/(2*4)+1/(3*5)+……+1/(10*12)

　　=1/2*[(1/1-1/3)+(1/2-1/4)+(1/3-1/5)+……+(1/10-1/12)]

　　=1/2*(1+1/2-1/11-1/12)

　　=1/2*175/132

　　=175/264