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If you simply send a letter, so will all the others, 20 letters equals no prize. If you don't, no one will, no prize.
So, you must introduce a random element, not controlled by yourself. For example, send a letter with the address slightly wrong, or with slightly insufficient postage. Different post offices will handle this differently, and most likely some, but not all, of the letters will arrive. That gives you a chance at the prize.
A more methodic approach is to base your decision of whether to send a letter or not on a random event, such as rolling dice. All the others will roll dice too, but will get different results, so only some will send letters.
To maximise your probability (as someone suggested in the comments) roll a "d20" - a 20 sided die - and only send the letter if you roll a 20. A probability calculation shows that this yields the best odds, with a surprising 37.7% chance that only one of you will roll a 20 and send a letter. Better odds than predicting post office behaviour, surely! |
