# M7.4.5

**Determines probabilities**using counting procedures, tables, trees, area models, and formulas for permutations and combinations.

### Confidence in Medical Tests

Medical tests are not always correct. When a doctor and a patient receive the rnresults of a test, what is the probability that the report is correct?

### Probability and Traffic Signals

It seems that traffic flow problems are becoming more and more common these days. In fact, despite the most noble efforts of city planners, even when there is very little traffic on the road, waiting seems to be a fact of life. So what is the probability that you will have to wait at a particular traffic signal, or perhaps more appropriately, what is the average amount of time you can plan on waiting? Let's look at a simple probability analysis related to traffic lights to find out.

### Corrupted Politicians

You can find statistics in every day life. Counting problems arise in situations where selections are made as in the following example of corrupted politicians.