1/1*2+2/1*2*3+3/1*2*3*4+……+9/1*2*…*10
=1-1/2+(1/1*2-1/2*3)+(1/1*2*3-1/2*3*4)+.+(1/1*2*3*...9-1/2*...10)
=1-1/2*3...10
=1-1/3628800
=3628799/3628800