Talk:Three-Day Math Points Challenge/@comment-174.134.220.112-20140914053845/@comment-24808864-20140914054740

It "seems" like it is random so far.

My guess is they divided users into three groups:

Group1: Invited to solo challenges

Group2: Invited to group challenges

Group3: Control group, no invites

If this is correct, it unfortunately seems you are in group 3.