A laboratory worker finds that 1.4% of his blood samples tested positive for the HIV virus.How many blood samples should he expect to test before finding one which tests positive for the HIV virus?
A)1.01
B)71.43
C)0.986
D)1.4
E)98.6

Question

Quizplus · Accepted Answer

We can use the formula for expected value:
expected value = 1/probability of success
In this case, the probability of success is 0.014 (1.4% written as a decimal). 
Therefore, expected value = 1/0.014 = 71.43
So the laboratory worker should expect to test about 71.43 blood samples before finding one that tests positive for the HIV virus.

A Laboratory Worker Finds That 1