
-1/5*6-1/6*7-1/7*8-1/8*9-1/9*10
=-(1/5-1/6)-(1/6-1/7)-(1/7-1/8)-(1/8-1/9)-(1/9-1/10)
=1/6-1/5-1/6+1/7-1/7+1/8-1/8+1/9-1/9+1/10
=-1/5+1/10
=-1/10

-1/5*6-1/6*7-1/7*8-1/8*9-1/9*10
=-(1/5-1/6)-(1/6-1/7)-(1/7-1/8)-(1/8-1/9)-(1/9-1/10)
=1/6-1/5-1/6+1/7-1/7+1/8-1/8+1/9-1/9+1/10
=-1/5+1/10
=-1/10