Final answer:
The information provided does not include data about the number of cows used in a typical burger from the documentary Food Inc.
Step-by-step explanation:
The question inquires about the content of a typical hamburger as depicted in the documentary Food Inc..However, the information provided does not directly answer the question about the number of cows contributing to a single burger.
From the provided reference materials, there appears to be no information that specifies the number of cows used in a typical burger. The references discuss the general practices of cattle farming and consumption patterns of beef, but not the specific detail about the composition of a burger. Without factual data from the documentary Food Inc. or a similarly credible source, it is not possible to provide an accurate answer to this question.