How do I calculate conditional probabilities using?Bayes’ Theorem?
Start by?drawing a tree diagram
Label?B1?&?B2?(&?B3?if necessary) on the?first set?of branches
Label?A?&?A’?on the?second set?of branches
The questions will give you enough information to?label the probabilities?on this tree
Identify the probabilities needed?to use Bayes’ Theorem
Exam Tip
In an exam you are less likely to make a mistake when using the formula if you draw a tree diagram first
Worked Example
Lucy is doing a quiz. For each question there’s a 45% chance that it is about music, 30% chance that it is about TV and 25% chance that it is about literature. The probability that Lucy answers a question correctly is 0.6 for music, 0.95 for TV and 0.4 for literature.
a)? ? ? ?Draw a tree diagram to represent this information.
b)? ? ? ?Given that Lucy answered a question correctly, find the probability that it was about TV.