Final answer:
To estimate the maximal number of identical books in a tipping stack, the primary necessary variable is the Number of books, with the physical dimensions like width and depth of each book also being relevant. The Total weight is less directly relevant, and the types of books are irrelevant as the books are identical.
Step-by-step explanation:
To formulate a system of equations for a problem where a group of students is stacking a set of identical books, each one overhanging the one below it by 1 inch, with the goal of estimating how many books they could place on top of each other before the stack tipped, several variables are relevant.
Option A, the Number of books, is crucial because it represents the total count of books in the stack which directly affects the stability of the stack. Option B, the Total weight, is less directly relevant to the tipping point unless the weight affects the friction between the books and the surface they are on. However, for just the tipping calculation, weight is not required since the problem assumes identical books (with presumably the same weight). Options C and D, the Number of Algebra books and the Number of Geometry books, are not necessary here as the books are stated to be identical, which implies that the type of book does not matter for the calculation of the stack's stability.
The variables that should be defined to formulate the system of equations are related to the physical dimensions of the books since the overhang, and therefore the tipping point, would be influenced by factors like the width and depth of the books. The mass of the book and the distance each book overhangs would be valuable to know. These variables relate to the stability and balance of the stack.