1-5/12+8/15+1/12-11/15-1/6
=1-（5/12-1/12）-（11/15-8/15）-1/6
=1-1/3-1/5-1/6
=2/3-1/6-1/5
=4/6-1/6-1/5
=1/2-1/5
=5/10-2/10
=3/10