you are the head of the Secret Service and the President
is about to arrive in Europe, where he will spend
Monday in Lisbon, Tuesday in Madrid, Wednesday in
Rome, Thursday in Prague and Friday in Paris. But
just before he departs on Sunday night, you received
intelligence from a source that an assassin plans
to attempt to assassinate the President on one of
those five days in one of those five cities. You
further are told that you will not know which day
or which city before the President arrives in that
city on that day.
the information is accurate, can any of these cities
be logically ruled out as the possible place of
the attack? If so, which one(s) are safe for the
President to visit?