小学生简便运算（要有过程）

1/6+1/12+1/20+1/30+1/42
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1/2-1/7
=7/14-2/14
=5/14

1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90
=1-1/2-1/3+1/3+1/4-1/4-1/5+........+1/9+1/10
=1-1/2+1/10
=1/2+1/10
=5/10+1/10
=6/10
=3/5

1.=(1/6+1/12)+(1/20+1/30)+1/42
=1/4+1/12+1/42
=1/3+1/42
=5/14

1、1/6+1/12+1/20+1/30+1/42
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=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
2、1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90
=1-1/2-1/3+1/3+1/4-1/4-1/5+........+1/9+1/10
=1-1/2+1/10
=1/2+1/10
=5/10+1/10
=6/10
=3/5