maxdancona wrote: "PuzzledPerson is clearly incorrect."
That's an assertion, not a refutation.
You have 1000 cents, of which 100 are dated before the Second World War, and you mix them thoroughly, then lay them out. Now you extend ten fingers and lay them simultaneously and blindly on 10 of the coins. What are the odds that at least one of them is pre-war?
Each finger, considered individually, has a 1 in 10 chance of resting on a pre-war coin, since out of 1000, 100 (or one-tenth) are pre-war. Since you have ten fingers, you have ten chances, each with a 1/10 probability of resting on a pre-war cent. That gives you a 10/10 = 100% probability that at least one of your fingers will select a pre-war cent. You may not pick one in actuality, but those are the odds.
Now what's wrong with that, specifically?