Three. One to get the punchline, and one to point out the math is wrong.
A magnetic banana.
A Joke "
Said the man in the pub to the bear. First heard this joke told by Eddie Izzard.
Yes.
Seven.
Ten. (Shame this one doesn't work too well for reddit - the funniest part of this joke is the third punchline enjoying people struggle to understand what the hell you're talking about.)
Punchlines that got married and settled down.
x always equals 10
They have trouble forming solutions.