There are only 10 sorts of people: those who understand binary and those who don't.

A biologist, a physicist and a mathematician went to investigate a mysterious house.  They looked around and no-one was inside, so they went outside and kept a watch on it.  After a few minutes two people went in.  A few minutes more and, strangely,  three people came out.

The biologist said 'They must have bred in there.'

'I think', said the physicist, 'that it must be an artefact of our measuring system, we must have miscounted.'

'What we need', said the mathematician, 'is for one person to go into the house and then it will be empty again.'