Question

2分之1加6分之1加12分之1加20分之1用简便算法算 快 快 8点之前 ok ok

Answer 1

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