原式=1/2+1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9+1/9+1/10
=5/6+1/3+1/10
=25/30+10/30+3/30
=38/30
=19/15