Irish Math

Q: In what town lives the mathematician who can only multiply by two?
A: Dublin.

Flight Risk

A mathematician and a non-mathematician are sitting in an airport hall waiting for their flight to go. The non- has terrible flight panic.
"Hey, don't worry, it's just every 10000th flight that crashes."
"1:10000? So much? Then it surely will be mine!"
"Well, there is an easy way out. Simply take the next plane. It's much more probable that you go from a crashing to a non-crashing plane than the other way round. So you are already at 1:10000 squared."

Noah Multiply

After the flood, Noah tells the animals from the Arc to "go forth and multiply."
After a few months, Noah figures he better wander around and see how the animals are doing. Everybody is happy until he comes across a couple of snakes - they are quite downcast and not very happy. Noah asks what wrong, and they say "We are Adders, so we can't multiply!"
Noah rubs his chin for a few moments, and then goes into the forest, cuts down a couple of trees, and makes a table out of them.
Then he puts the snakes up on the platform he has made, and says "Now you should be happy. Everybody knows that adders can multiply with log tables!"