Carol was sending out birthday invitations to 18 friends. She bought 6 packs each one having the same number of invitations. How many invitations are in each pack?
Carol is sending out 18 invitations. 
She bought 6 packs. 
Each pack has the same number of invitations. 

That means that if we divide 18 by 6, we'll know how many invitations are in each pack. 

18 divided by 6 equals 3. 

So, each pack has 3 invitations.