MathDB
Putnam 2001 A2

Source:

February 26, 2012
Putnamprobabilityfunctioninductionrational functioncollege contests

Problem Statement

For each kk, Ck\mathcal{C}_k is biased so that, when tossed, it has probability 1(2k+1)\tfrac{1}{(2k+1)} of falling heads. If the nn coins are tossed, what is the probability that the number of heads is odd? Express the answer as a rational function nn.