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#1 2010-01-28 02:03:39
- katerinaaa
- Novice
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problem with probabilities
Hi all, I have a problem with probabilities but I can't solve it.
The problem is :
"I have 3 folders. A folder of them has a letter while the others are empty.
The probablity to find the letter in the folder, if we touch the top of the folder is p_j , if there is letter in this folder.
We check folder 1 and we did not touch the letter.
Which is the possibility the letter to be inside the folder 1 ??"
I don't understand, the possibility is 1/3 again I think.
Could you help me please ??
thanks a lot
#2 2010-01-28 13:19:07
- bobbym
- Administrator
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Re: problem with probabilities
Hi katerinaaa;
Are asking what is the probability of choosing a folder with the letter in it if there are 3 folders and only one folder has a letter in it?
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#3 2010-01-29 08:24:28
- mathsyperson
- Moderator
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Re: problem with probabilities
Three things could have happened:
1) The letter is in folder 1, and you missed it when you checked earlier.
This has probability 1/3 * (1-p_j).
2) The letter is in folder 2. This has probability 1/3.
3) The letter is in folder 3. This also has probability 1/3.
And for completeness:
[4) The letter is in folder 1, and you found it earlier. Probability 1/3 * p_j.]
We already know the 4th option didn't happen, so the probability of the letter being in folder 1 is
or more simply,
This means that the probability of the letter being in folder 1 is:
1/3, if p_j = 0.
0, if p_j = 1.
1/5, if p_j = 1/2.
etc.
Why did the vector cross the road?
It wanted to be normal.
#5 2010-09-07 21:26:11
- leealden06
- Novice
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Re: problem with probabilities
In probability, the problem of birthday, or accession to the birthday paradox probability that a number of people chosen at random for a couple of them have the same problem birthday.The is to calculate approximately the probability that a room of people, have at least two the same birthday.
#6 2010-09-08 06:12:26
- bob bundy
- Moderator
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Re: problem with probabilities
hi leealden06
I've met this before. Are you asking how to calculate this?
Bob
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#7 2011-02-27 17:40:38
- frankMwarimbo
- Novice
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Re: problem with probabilities
whats is the difference between independent events and dependent event?
#8 2011-02-27 18:19:03
- bobbym
- Administrator
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Re: problem with probabilities
Hi frankMwarimbo;
Two events are independent if the occurrence of one has no effect on the probability of the other.
Please take a look here:
http://www.mathsisfun.com/definitions/i … event.html
http://www.mathsisfun.com/data/basic-co … ciple.html
http://www.learningwave.com/chapters/pr … ndent.html
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.