Carol was sending out birthday invitations to 4 friends. If each package of invitations she bought had 105 invitations in it How many packs does she need so that no friend gets left out?
Carol wants to invite 4 friends to her birthday party. 
Each package of invitations has 105 invitations in it. 

So we need to find out how many invitations are in 4 packages. We can do this by multiplying 105 and 4. 

105 x 4 = 420 

So Carol needs to buy 4 packages of invitations so that no friend gets left out.