Agenetic test is used to determine if people have a predisposition for thrombosis, which is the formation of a blood clot inside a blood vessel that obstructs the flow of blood through the circulatory system. it is believed that 3% of people actually have this predisposition. the genetic test is 99% accurate if a person actually has the predisposition, meaning that the probability of a positive test result when a person actually has the predisposition is 0.99. the test is 98% accurate if a person does not have the predisposition. what is the probability that a randomly selected person who tests positive for the predisposition by the test actually has the predisposition?

The probability that a randomly selected person that tests positive for the predisposition by the test actually has the predisposition is : 0.6

i.e. P( Disease | positive ) = 0.6

Let : B = positive , A = disease

∴ P( A | B ) = P( B | A ) P ( A ) / P( B )

where : P( B | A ) = 0.99

             P ( A ) = 0.03

∴ P(Disease | positive ) = P ( positive |  disease ) * P( disease ) / P ( positive )

                                        =   (0.99) * (0.03) / P(positive )   ( 1 )  

Also  P( Positive ) = P( B | A ) P( A )+ P( B | no disease

)* P( no disease )  

                             = (0.99)*(0.03) + (0.02)* (0.97) = 0.049 ( 2 )

back to equation ( 1 )

P( Disease | positive ) = (0.99)* (0.03) / (0.049) = 0.6.

Hence the probability that a randomly selected person person who tests positive has the predisposition is 0.6

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the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.