Consider the recursive relationship for combinations:
C(n,r) = C(n-1,r) + C(n-1,r-1)
Prove this relationship algebraically using the mathematical definition of a combination, as well as that of the factorial function.
Provide a logical explanation for this relationship (Hint: consider n objects as consisting of n-1 existing objects plus a new nth object. Given the ultimate goal of selecting r objects from the entire set of n, you must select objects from the set of n-1 objects and decide how the new nth object should join the existing selected sets.)