By making the surface rougher and to increase the force pushing the surfaces together.
        
                    
             
        
        
        
You can buy 23 salads because the group wants 12 instead of 15 15-12=3
        
                    
             
        
        
        
You divide 14.99 by 5 which is 2.998. 1/5 off of 14.99 would be $ 11.99 rounded, because you subtract the 2.99 on 14.99