Question on a math test:

If you choose a random answer to this question, the probability that you’ll be correct is:
a) 25% b) 66% c) 50% d) 25%

The first option looks good. Four answers, one in four, 25%. Some people stop there and move on. But they’re wrong. Why? There are two answers that have 25%, and random choice gives that even odds — 50%. So obviously the correct answer is c… except if it is, the odds are back to 25% again.

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