\begin{problem}[10]
Consider the following variation of the Monty Hall game: as usual
there are three doors and a prize hidden behind one door.  But now the
contestant picks \emph{two} doors and Monty's assistant opens one of
the two chosen doors that does not have a prize behind it.

Should the contestant use a strategy of sticking with the unopened door of
the two he chose, or switching to the unchosen door, or doesn't it matter
in this version of the game?

State your answer and indicate the probability the contestant will win
using your strategy.  No explanation is required.

\solution{
Contestant should stick.  Contestant wins whenever prize is behind one
of his two chosen doors, and probability of this is 2/3.  }

\end{problem}
