Answer to Question #201046 in Statistics and Probability for Lou Robert Cuyos

Question

In a viral pool test it is known that in a group of five (5) people, exactly one (1) will test positive. If they are tested one by one in random order for confirmation, what is the probability that only two (2) tests are needed? 

Answer 1

The first occurrence of success requires 2 trials

$$P=(1-\dfrac{1}{5})(\dfrac{1}{5-1})=\dfrac{1}{5}$$