Pat works in the city and lives in the suburbs
with Sal. Every afternoon, Pat gets on a train that arrives
at the suburban station at exactly 5 P M . Sal leaves
the house before 5 and drives at a constant speed so as
to arrive at the train station at exactly 5 P M to pick up
Pat. The route that Sal drives never changes.
One day, this routine is interrupted, because there
is a power failure at work. Pat gets to leave early, and
catches a train which arrives at the suburban station
at 4PM. Instead of phoning Sal to ask for an earlier
pickup, Pat decides to get a little exercise, and begins
walking home along the route that Sal drives, knowing
that eventual ly Sal will intercept Pat, and then will
make a V-tum, and they will head home together in
the car. This is indeed what happens, and Pat ends up
arriving at home 10 minutes earl ier than on a normal
day. Assuming that Pat 's walking speed is constant,
that the V-tum takes no time, and that Sal 's driving
speed is constant, for how many minutes did Pat walk?