BUT it is wrong.
I heard this back in the 70s.
It goes something like this.
a person asked an accountant, an engineer and an economist how much 2 plus 2 is.
There are three punchlines depending on whether your audience is economists, accountants or engineers.
We will take the audience of economists.
The engineer gets out his slide rule ( yes it is that old) and says the answer is 4.0000000000000
The accountant looks smugly and answers how much do you want it to be.
the economist says let us assume.....
get it!!
Catallaxy can't even get jokes accurate. Says it all really.
Update
A mate has just e-mailed me to say he remembers me repeating this joke only in an updated way after one of my lectures in my first year at business school. The class made up up mostly of engineers and some accountants, only one economist though.
Don't e-mail, comment!!