“Here’s one way to think about a 1-in-10,000 daily chance: It would take more than three months for the combined risk to reach just 1%,” according to The New York Times.
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Someone doesn’t understand probabilities. A 1-in-1000 daily chance is always a 1-in-1000 daily chance. It’s like flipping a penny. Every flip is a 50-50 chance of “heads”.
The chance of not getting infected over three months is (1-0.0001) to the 90th power.
The chance of not flipping tails with a daily flip over three months is 0.5 to the 90th power, which is vanishingly small.
“A 1-in-1000 daily chance is always a 1-in-1000 daily chance. It’s like flipping a penny. Every flip is a 50-50 chance of “heads”.
You are right that if you flip a coin once a day, your chance of getting heads on any one of those days is 50/50 or 1-in-2.
But if you flip a coin each day for ten days, your chances of getting heads on at least ONE of those days is almost 100%:
1-(1/2)^10 which equals 1023/1024
So, if you have a 1/1000 chance of getting sick on any given day, then your chances of getting sick over 90 days is 1-(1/1000)^90 an EXTREMELY high probability.