If there were 150 members in the group before the admin removed 20, then 150-20 = <<150-20=130>>130 members remained after 20 were removed.
The group members each posted 50 messages in a day, a total of 50*130 = <<50*130=6500>>6500 messages.
In a week, with seven days, the group members would have posted 6500*7 = <<6500*7=45500>>45500 messages
#### 45500