An engineer, a scientist and a mathematician are each sent in a room with nothing in it but a tin can and a chalk stick with the task to open the tin can in one hour.
The rooms are checked after one hour:
The engineer’s room is covered in impact notches, with the successful one circled with the chalk, and the engineer is holding the opened can.
The scientist’s room is half covered in calculations, with a few impact notches concentrated around the same spot as the engineer. The scientist is also holding an opened can.
The mathematician’s room is entirely covered in complex calculations, a single notch is visible, the tin can is closed and the mathematician is missing.
As the scientist tries to decipher the writings, the tin can starts shaking. The engineer grabs it, smashes it open on the wall and the mathematician is ejected from inside the can.
“holy #&@$!”, he said, “I must have missed a minus sign somewhere”