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May 12th, 2011, 11:35 PM   #1
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Probability question (hard and confusing)

1. A new skin test is devised for detecting tuberculosis. To evaluate the test before it is put into use, a research indicates tuberculosis in 96% of those who have it and in 2% of those who do not. It is known that 8% of the population have tuberculosis.

a) What is the probability of a randomly selected person having tuberculosis given that the skin test is positive?
b) What is the probability that a person has tuberculosis given that the test indicates no tuberculosis is present?
c) What is the probability of the skin test giving a false positive result?

2. A box contains 6 green balls and 4 red balls. 3 balls are chosen at random. Find the probability of obtaining exactly 2 green balls and 1 red balls are chosen

a) with replacement
b) without replacement

3. A carton of 12 eggs contains 3 eggs with double yolks. If 4 eggs are selected at random from the carton, without replacement, find the probability that exactly 2 eggs have double yolks.

I am quite good in probability, but when comes to these question, I can't solve it and dunno how to start to solve it. I need help and explanation for the question. Thank you.
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May 13th, 2011, 03:09 AM   #2
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Can you make some attempt (for any of the questions)? Have you been told what the answers should be?
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May 13th, 2011, 06:05 AM   #3
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Re: Probability question (hard and confusing)

For question 2

a) 2/10 x 1/10

b) 2/10 x 1/9

other I dunno how to do. I need help and explanation.
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May 13th, 2011, 11:10 AM   #4
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Re: Probability question (hard and confusing)

Hello, hoyy1kolko!

Quote:
2. A box contains 6 green balls and 4 red balls.
Three balls are chosen at random.
Find the probability of obtaining exactly 2 green balls and 1 red balls.

a) with replacement

Since the balls are replaced, the probabilities are independent.






Quote:
b) without replacement






[color=beige]. . [/color]




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May 13th, 2011, 05:20 PM   #5
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Re: Probability question (hard and confusing)

Thank you sir, I get the concept now. How about question 1 and 3?
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May 15th, 2011, 02:14 AM   #6
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Are you familiar with the law of total probability and with Bayes's theorem? If so, can you apply these to question 1(a)?
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May 15th, 2011, 04:58 AM   #7
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Re: Probability question (hard and confusing)

can you explain the concept briefly to me?Thank you.
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May 18th, 2011, 12:03 AM   #8
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Re: Probability question (hard and confusing)

I need help.
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May 18th, 2011, 06:37 AM   #9
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Re: Probability question (hard and confusing)

Hello, hoyy1kolko!

I'm sorry, but I must point this out.

#2 involves colored balls; #3 involves eggs.
[color=beige]. . [/color]Other than that, the problems are the same.

If you can't transfer a procedure from one problem to another,
[color=beige]. . [/color]you need more help than any of us can provide.

I've solved and explained about a dozen probability problems for you.
You seem to have learned nothing and keep asking identical questions.

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May 18th, 2011, 08:49 AM   #10
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Re: Probability question (hard and confusing)

Thank for your advise,sir.I will try to solve the question and post the working for you.
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