Let $ n \geq 2, n \in \mathbb{N}$ and let $ p, a_1, a_2, \ldots, a_n, b_1, b_2, \ldots, b_n \in \mathbb{R}$ satisfying $ \frac{1}{2} \leq p \leq 1,$ $ 0 \leq a_i,$ $ 0 \leq b_i \leq p,$ $ i = 1, \ldots, n,$ and \[ \sum^n_{i=1} a_i = \sum^n_{i=1} b_i.\] Prove the inequality: \[ \sum^n_{i=1} b_i \prod^n_{j = 1, j \neq i} a_j \leq \frac{p}{(n-1)^{n-1}}.\]
Problem
Source: IMO ShortList 1991, Problem 26 (CZE 1)
Tags: Inequality, algebra, polynomial, n-variable inequality, IMO Shortlist