MathDB
Putnam 2006 B4

Source:

December 4, 2006
Putnamanalytic geometryvectorinductionlinear algebracollege contests

Problem Statement

Let ZZ denote the set of points in Rn\mathbb{R}^{n} whose coordinates are 00 or 1.1. (Thus ZZ has 2n2^{n} elements, which are the vertices of a unit hypercube in Rn\mathbb{R}^{n}.) Given a vector subspace VV of Rn,\mathbb{R}^{n}, let Z(V)Z(V) denote the number of members of ZZ that lie in V.V. Let kk be given, 0kn.0\le k\le n. Find the maximum, over all vector subspaces VRnV\subseteq\mathbb{R}^{n} of dimension k,k, of the number of points in VZ.V\cap Z.