What was a significant achievement of Five Guys within 18 months of starting franchising?

The significant achievement of Five Guys within 18 months of starting franchising was the selling out of franchise territory. This accomplishment demonstrates the brand's rapid growth and strong demand in the market shortly after launching its franchising model. Selling out territory indicates that the company successfully attracted a number of franchisees eager to invest in and operate Five Guys locations. This level of enthusiasm from franchisees reflects confidence in the brand's business model, its menu offerings, and overall popularity with customers. Additionally, this milestone can serve as a strong indicator of the company's brand strength, market presence, and effective franchise support system, which are all vital components for successful expansion in the food industry.

The other options represent potential growth strategies or achievements, but they did not occur specifically within that initial 18-month franchising period. For instance, while opening 100 locations could signify growth, selling out territory showcases immediate interest and commitment from franchisees, which is essential for sustainable expansion.