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Computer Science
Take Home Exam: Bayes Nets and Knowledge Representation
Silent Policy: A silent policy will take effect 24 hours before this assignment is due, i.e. no questions will
be answered, whether asked on the discussion board, via email or in person.
Policies:
1. The TAs and instructors will continue to hold office hours and host help sessions between April 3rd
and the due date. However, during these sessions, you may not discuss problems on the take home
exam. Instead, you can discuss practice problems that have been posted to the website. Similarly,
on Piazza, you may not discuss problems on the take home exam. You can instead discuss practice
problems.
2. You must work alone on this take home exam. You may not discuss problems on the take home
exam with anyone (including other students).
3. You must write your answers clearly and legibly for full marks.
4. No submissions will be accepted past the due date without approval.
5. There will be no auto-fail policy associated with this exam.
Total Marks: This exam represents 20% of the course grade.
Handing in this Assignment
What to hand in electronically: Submit written answers in a file called answers.pdf as well as
acknowledgment form.pdf using MarkUs. Your login to MarkUs is your teach.cs username and password.
It is your responsibility to include all necessary files in your submission.
Clarification Page: Important corrections (hopefully few or none) and clarifications to the assignment
will be posted on the Exam Clarification page, linked from the CSC384 web page, also found at: http:
//www.teach.cs.toronto.edu/~csc384h/winter/tests.html. You are responsible for monitoring
the Exam Clarification page.
Questions: Questions about the exam should be asked on Piazza:
https://piazza.com/utoronto.ca/winter2020/csc384/home.
You may also reach out to the TAs or one of the instructors. Please place ”Exam” and ”CSC384” in the
subject line of your email.
Q1. Probability (worth 15/100 marks)
1. (worth 2 marks) There is a type of skin cancer that affects 3 in every 100 people. A company has
invented a test that can diagnose this cancer using an image. The test isn’t perfect, tho; it will give a
false positive (i.e. it will detect cancer when there is none) 5% of the time and a false negative (i.e.
it will fail to detect a cancer that is present) 3% of the time.
If a test is positive, what is the probability the patient does not have cancer? If a test is negative,
what is the probability the patient does have cancer?
2. (worth 3 marks) Doctors are not happy with the false positive rate of the test. The company responds
by creating a new test that has a false positive rate of 6% and false negative rate of 4%. Although the
test seems worse than the original, the company explains the test results are conditionally independent
of one another given the condition of the user. They suggest using both tests in conjunction to
improve the false positive rate. Specifically, they suggest doctors diagnose cancer if and only if both
tests are positive. Does this logic make sense? Explain.