简便运算:2/3 +7/12+ 9/20 +11/30+ 13/42=?
问题描述：
简便运算:2/3 +7/12+ 9/20 +11/30+ 13/42=?
答
2/3=1-1/3
7/12=4/3-3/4
9/20=5/4-4/5
...下面2个也是一样的拆法
然后同分母的相互加减
答
题目只有这样才能简便运算吧：
2/3 +7/12- 9/20 +11/30- 13/42
=(1-1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1-1/7
=6/7