the change (or lack thereof) in the probability of something inevitable occurring as time goes on

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(I wasn’t able to find this specific question, so sorry if it’s been asked before)
Earlier today, I was told I would get a call between 5:00 and 6:00. If we make the assumption that this call is, for certain, going to occur within the specified time frame, I was under the assumption that every minute that passed would result in an increase in probability of the call would happen. For example, I was thinking that for the first minute the chance I get the call are 1/60, while the second minute would be 1/59 (as there are now only 59 minutes in which it could happen) and so on until the last minute is 1/1 (if I had still not received the call).
However, I was thinking back to my Freshman statistics course where my professor was talking about how the chances of the event happening at any given moment are the same, regardless of what time it is. In this case, at any given minute, the chance of me getting a call would still be 1/60. Unfortunately, I don’t remember any of the terminology that goes with these concepts, so I can’t remember if that actually applies to this problem.
So, in short, does the probability of something presumably inevitable increase as time passes? Or is the chance the same at any given moment?

In: Mathematics

8 Answers

Anonymous 0 Comments

there are dependent and independent variables.

A coinflip is independent, each coinflip does not depend on the previous one, so the odds of getting a heads after 10 tails is still 50%

A bag of marbles is dependent, each marble you pull out reduces the number of marbles in the bag. So if there was a bag of 11 marbles, 10 red, and 1 blue, there is a 1/11 chance of pulling a blue marble on the first pull, but a 100% chance of pulling it on the last pull if you previously pulled 10 reds.

The phone example is more like a bag of marbles. at the beginning of the hour, its 1/60 for any given minute, but as the minutes wear on with no call, the probability increases for each future minute because getting a call is dependent on not having already got a call.

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