Final answer:
The default fountain drink size given when a customer does not specify is usually the establishment's standard or medium size, potentially ranging from 12 to 16 ounces, to balance cost and customer satisfaction.
Step-by-step explanation:
If a customer does not specify a fountain drink size, what is typically provided is the establishment's standard or default size. This size is often determined by the vendor's most commonly sold size or could be based on what is considered a medium in the general market. In absence of a specified size, some businesses might opt to serve a size that balances cost with customer satisfaction, or they might default to a small size to avoid customer complaints about being overcharged. In the beverage and food industry, consistency is essential for customer satisfaction and inventory control, hence having a default size helps in maintaining standardization. Beverage sizes at food service establishments are measured in fluid ounces, and the default size could range anywhere from 12 to 16 ounces, depending on the vendor's practices.