Dirty Bomb - S1-E10
Factual error: Season 1, Episode 10, "Dirty Bomb": The opening figures refer to "500g of Nuclear Material." These are the wrong units to determine the hazard level in a radiological sample. The "Curie content" describes, roughly, how much radiation will be given off, and is not tied directly to the sample's mass. 500g of Cesium-137 (the isotope being discussed in the episode) could well be less radioactive than 1g of a different isotope.
Dirty Bomb - S1-E10
Continuity mistake: When Charlie is writing the result of the calculation for the first time he writes "25,600", but when the shot changes he finishes writing "25600", without a comma.
Answer: Craps is a casino game where players bet on the outcome of a dice roll. It deals heavily with probabilities and is a favorite of math experts like Charlie. Whatever the odds, though, your chances of winning are much greater than winning the lottery.
If you bet against the roller in craps, your odds of winning are about 49%, which is as good as you get in Vegas. The point he's making (though it's pretty obscure) is that if you're going to bet, you may as well bet on something where you have a slim chance of winning, as opposed to the lottery, where your chances are basically 0.