化简:1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10

=(1-1/2)+(1/2-1/3)+.+(1/9-1/10)
=1-1/2+1/2-1/3+1/3-...-1/9+1/9-1/10
=1-1/10
=9/10