1/2-1/6-1/12-1/20-1/30-1/42=?是6/7 还是1/7
问题描述：
1/2-1/6-1/12-1/20-1/30-1/42=?是6/7 还是1/7
答
1/2-1/6-1/12-1/20-1/30-1/42
=2/6-1/12-1/20-1/30-1/42
=1/4-1/20-1/30-1/42
=1/5-1/30-1/42
=1/6-1/42
=6/42
=1/7