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May 13th, 2011, 12:35 AM  #1 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  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. 
May 13th, 2011, 04:09 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,980 Thanks: 1852 
Can you make some attempt (for any of the questions)? Have you been told what the answers should be?

May 13th, 2011, 07:05 AM  #3 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  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. 
May 13th, 2011, 12:10 PM  #4  
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 407  Re: Probability question (hard and confusing) Hello, hoyy1kolko! Quote:
Since the balls are replaced, the probabilities are independent. Quote:
[color=beige]. . [/color]  
May 13th, 2011, 06:20 PM  #5 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  Re: Probability question (hard and confusing)
Thank you sir, I get the concept now. How about question 1 and 3?

May 15th, 2011, 03:14 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 19,980 Thanks: 1852 
Are you familiar with the law of total probability and with Bayes's theorem? If so, can you apply these to question 1(a)?

May 15th, 2011, 05:58 AM  #7 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  Re: Probability question (hard and confusing)
can you explain the concept briefly to me?Thank you.

May 18th, 2011, 01:03 AM  #8 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  Re: Probability question (hard and confusing)
I need help.

May 18th, 2011, 07:37 AM  #9 
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 407  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. 
May 18th, 2011, 09:49 AM  #10 
Senior Member Joined: Dec 2010 Posts: 233 Thanks: 0  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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