7/13−1/12−5/12 +6/13=(7/13+6/13)-(1/12+5/12)=1-1/2=1/2
7/13−1/12−5/12+ 6/13=(7/13+6/13)-(1/12+5/12)=1 -1/2=1/2
7/13-1/12-5/12+6/13=(7/13+6/13)-(1/12+5/12)=1-1/2=1/2
