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January 30, 2015

January 30, 2015

Posted by **Anonymous** on Wednesday, February 11, 2009 at 2:47pm.

a) What is the probability that both test yield the same result?

B) If both tests are positive, what is the probability that the selected individual is a carrier?

i have no idea on where to start.

- statistics -
**economyst**, Wednesday, February 11, 2009 at 4:20pmExcel spreadsheets are very helpful for these kinds of problems.

Start by building a probability tree, calculate all possible values. There are 2 kinds of people (with and without), and each test has two answers (yes, no). So, there should be 8 possible outcomes.

The probability of seeing a person with the disease and both test positive is: .01*.9*.9 = .0081

of seeing a person with the disease and the first test is positive and the second negative = .01*.9*.1 = .0009

Repeat for the other 6 possibilities. If you did the calculations right, the sum of the 8 values should be 1.0.

Then you will have all the information you need.

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