The only evidence we have for the “Americans were too stupid to understand that 1/3 was bigger than 1/4” story is from the memoirs of the A&W CEO at the time referencing some unnamed market research performed by some unnamed firm. A person who has a vested interest in explaining why their failure to turn around a sinking company was due to external factors beyond their control. It also implies that in a culture where every kitchen has at least one set of stackable measuring cups in 1/4, 1/3 and 1/2 sizes, and a culture where you would order meat from the deli counter at your grocery store in 1/4 or 1/2 lb increments was suddenly and completely incapable of remembering their basic fraction sizes when comparing the cost of a hamburger. Personally while it makes for a cute story, I really just don’t believe it.