Police often set up sobriety checkpoints—roadblocks where drivers are asked a fe
ID: 3378778 • Letter: P
Question
Police often set up sobriety checkpoints—roadblocks where drivers are asked a few brief questions to allow the officer to judge whether or not the person may have been drinking. If the officer does not suspect a problem, drivers are released to go on their way. Otherwise, drivers are detained for a Breathalyzer test that will determine whether or not they will be arrested. The police say that based on the brief initial stop, trained officers can make the right decision 80% of the time. Suppose the police operate a sobriety checkpoint after 9 p.m. on a Saturday night, a time when national traffic safety experts suspect that about 12% of drivers have been drinking.
a) What’s the probability that any given driver will be detained?
b) What’s the probability that a driver who is detained has actually been drinking?
Explanation / Answer
Police often set up sobriety checkpoints—roadblocks where drivers are asked a fe