An engineer and a mathematician are in a room with one door.

An engineer and a mathematician are in a room with one door. Both
of them are asked (one at a time) to go into the next room, where they
will find a pot of water and a stove, and boil the pot of water.
The engineer goes into the next room, sees the pot of water sitting
on a table, puts it on the stove, turns on the stove, and waits until
it boils. A little bit later (the room is reset for the mathematician),
the mathematician goes into the next room, sees the pot sitting on
the table, puts it on the stove, turns on the stove, and waits until
it boils.
Now both of them are asked to do this again. However, this time the
pot of water is on the floor. The engineer sees the pot of water on
the floor, puts it on the stove, and waits until it boils. The
mathematician, however, sees the pot of water on the floor, puts it
on the table and proclaims, "I've solved this problem already."