1-2/5-3/10.
=10/10-4/10-3/10
=3/10
8/11+3/13-8/11.
=8/11-8/11+3/13
=0+3/13
=3/13
1/5+1/3.
=3/15+5/15
=8/15
1/4+1/8.
=2/8+1/8
=3/8
1-2/5-3/10.
=10/10-4/10-3/10
=3/10
8/11+3/13-8/11.
=8/11-8/11+3/13
=0+3/13
=3/13
1/5+1/3.
=3/15+5/15
=8/15
1/4+1/8.
=2/8+1/8
=3/8