Distribution problems ask how to distribute objects into groups. For n identical objects into r distinct boxes (empty boxes allowed): C(n+r-1, r-1). For each box having at least one: C(n-1, r-1). These follow from the "stars and bars" visualization — n stars separated by r-1 bars. For upper-bound constraints (each box has at most k), use inclusion-exclusion. For n distinct objects into r distinct groups: if order within groups matters, it's a permutation problem; if not, use multinomial coefficient n!/(n1! * n2! * ... * nr!). If groups are unlabeled and equal-sized, divide further by the number of groups factorial. JEE commonly frames these as: "distribute 10 identical balls into 3 boxes" or "find non-negative integer solutions of x + y + z = n."