Carol was sending out birthday invitations to 30 friends. She bought 1 packs each one having the same number of invitations. How many invitations are in each pack?
Carol is sending out 30 invitations. 
She bought 1 pack of invitations. 
Each pack has the same number of invitations. 

So if she bought 1 pack of invitations, and each pack has the same number of invitations, that means that there is only 1 pack of invitations. 

Therefore, there are 30 invitations in each pack.