In a certain country 20\% of the population suffers from hay fever. People can
undergo a skin prick test to find out whether they have hay fever.

The skin prick test has a sensitivity of 75\%. This means that 75\% of the people
with hay fever, test positive on the skin prick test.

The skin prick test has a specificity of 90\%. This means that 90\% of the people
who don’t have hay fever, test negative on the skin prick test.

\nbPointsRegular{4}A person chosen at random undergoes the skin prick test. What is the probability
that this person has a positive test result?
