Select Multiple workbooks at once to perform an action

[rshnkmr39]

I have a main tab followed by 15 tabs.

I need to select all 15 tabs at once to perform a certain action at once.
i.e in all 15 tabs in particular cells addition,average etc will be performed.
How can I activate all 15 tabs(other than the main tab) and do this

[rshnkmr39]

The basic idea is to activate all 15 tabs other than the first tab