You have coins C1, C2, · · · , Cn. For each k, coin Ck is biased so that, when tossed, it has probability 1/(2k + 1) of falling heads.

If the n coins are tossed, what is the probability that the number of heads is odd?

Express the answer as a rational function of n.

Source: Putnam 2001

The required expression is:

Posted by K Sengupta on 2024-03-04 20:14:13