1/3+1/6+1/12+1/20
=1/3+1/2-1/3+1/3-1/4+1/4-1/5
=1/3+1/2-1/5
=10/30+15/30-6/30
=19/30题目写错啦那你改过来是不是1/2要是的话就是1/2+1/6+1/12+1/20=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5=1-1/5=4/5题目是：1/3+1/6+1/12+1/24麻烦了1/3+1/6+1/12+1/24=1/3+1/2-1/3+1/3-1/4+1/2×（1/4-1/6）=1/3+1/2-1/4+1/8-1/3+1/4=1/2+1/8=5/8