解:1+1/2--5/6+1/12--9/20+11/30--13/42
=3/2--5/6+1/12--9/20+11/30--13/42
=2/3+1/12--9/20+11/30--13/42
=3/4--9/20+11/30--13/42
=3/10+11/30--13/42
=2/3--13/42
=5/14。
原式=1+1/2-(1/2+1/3)+(1/3-1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1+1/2-1/2-1/3+1/3-1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1/2-1/7
=5/14
这马甲是?
3991/2520