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