Exam format, scoring and sample questions

Intuition

The exam is fifty questions with five tick-boxes each. You are not choosing one answer, you are deciding about every box. The scoring rule decides how bold to be.

The exam is 50 multiple-select questions with symmetric scoring

The Week 12 and 13 slides give the format. It is a supervised, in-person exam: 50 questions, 5 options each, 1 or more correct, with negative marking, answered on the supplied Gradescope MCQ answer sheet. The exam is worth 50% of the unit, and School of Computer Science policy is that you must get at least 40% of the exam marks to pass the unit (course info slides). The slides do not state the length. The course plan gives 2 hours, so check your timetable.

Exam detail

For a question with $k$ correct options: each correct option ticked scores $+\tfrac{1}{k}$, each wrong option ticked scores $-\tfrac{1}{k}$, and the question score has a floor of 0. If three options are correct, a correct tick is $+\tfrac13$ and a wrong tick is $-\tfrac13$. Ticking all correct options and no wrong ones gives exactly 1. Unticked options score nothing.

Try it: worked example

A question has k = 3 correct options. Find the score for each of: (a) 2 correct ticked and 1 wrong ticked, (b) 3 correct ticked and no wrong, (c) 1 correct ticked and 2 wrong ticked.

Show answer and steps

Answer(a) 1/3, (b) 1, (c) 0 after the floor

1. Each tick is worth 1/3 in size, so k = 3 gives +1/3 for correct and -1/3 for wrong.
2. (a) 2 x (+1/3) + 1 x (-1/3) = 2/3 - 1/3 = 1/3.
3. (b) 3 x (+1/3) + 0 = 1, the maximum.
4. (c) 1 x (+1/3) + 2 x (-1/3) = 1/3 - 2/3 = -1/3. The floor at 0 applies, so the question scores 0, not a negative number.

Tick an option when it is more likely right than wrong

Suppose you think an option is correct with probability $p$. Ticking it scores $+\tfrac1k$ with probability $p$ and $-\tfrac1k$ with probability $1-p$. The expected change in your score is

$\frac{1}{k}\,p - \frac{1}{k}\,(1-p) = \frac{2p-1}{k}.$

That is positive only when $p > 0.5$, zero at exactly 0.5, and negative below. Leaving the box blank has an expected change of zero. So on its own, a tick gains on average only when you believe the option is more likely correct than not. The value of $k$ only scales the stake, it does not move that break-even point.

The floor at 0 changes the picture for one case. The formula above ignores the floor, but the question score cannot go below 0. If you have no confident ticks on a question, a single guess can only help. Take $k = 2$ and one guess with $p = 0.2$: it scores $+ frac12$ with probability 0.2 and floors at 0 otherwise, an expected $+0.1$ against 0 for leaving the question blank.

Practical rule: tick every option you think is more likely right than not. On a question where you would otherwise tick nothing, tick your best guess. Do not add low-confidence guesses on top of confident ticks, because there the loss is real and the floor no longer protects you. You do not need to know $k$ for either rule.

Pitfall

Ticking everything is not safe. Ticking all 5 options when k = 2 gives 2 x (+1/2) + 3 x (-1/2) = -1/2, which floors at 0. You gain nothing over leaving the question blank, and you lose the chance to score.

What is examinable and what to bring

Examinable: contents of Lectures 1 to 10 inclusive, plus tutorials and assignments. The slides ask you to focus on understanding the topics, concepts and theories. The guest lectures are not on the Lectures 1 to 10 list, so the topics in Module 11 are marked non-examinable. Week 13 has a guest lecture by Dr Ying Ma plus exam revision.

Optional aside

Book rule. The Canvas course-info page described the exam as closed book. The Lecture 12 slide says “Restricted book exam, 1 A4 sheet of handwritten and/or typed notes double-sided”. Lecture 12 is the later and more specific source, so plan for one A4 sheet, double-sided. The site’s /cheatsheet page is a printable A4 double-sided sheet and a good starting point for your own.

Exam detail

Bring: one valid photo ID with your full name (University of Sydney student card, passport, Australian driver’s licence or Australian photo card; not expired; a digital Government ID on your phone is accepted if you have no physical ID, but not a picture, PDF or photocopy). Keep your student card visible on the desk. Pens, pencils and eraser. Small food items such as sweets or mints. A water bottle in a clear container. Your A4 sheet.

Do not bring: earplugs (ask if they supply them), a pencil case, a recording or scanning device, watches (analogue or digital), electronic devices, dictionaries. Bags go to the bag area and a phone left in a bag must be switched off.

Timing: you may enter 15 minutes before the start. You cannot leave in the first 30 minutes (reading time included) and are not admitted after 30 minutes. The supervisor tells you when you may start writing and when 10 minutes remain. You cannot leave in the last 10 minutes. Stay seated until papers are collected and counted. Raise your hand for the toilet, leaving belongings behind. Do not take the exam paper or any papers out.

Bringing unauthorised aids can lead to confiscation and misconduct proceedings under the University of Sydney (Student Discipline) Rule 2016, with penalties up to failure in the unit or exclusion.

The twenty sample questions below are the exam prep set, verbatim

The quiz on this page holds every sample question from the Week 13 exam prep slides, in the PDF’s wording, with the PDF’s stated answers. Questions 1 to 6 and 8 to 10 have four options, questions 7 and 11 to 20 have five. Each why begins with the PDF stated answer. Three keys look arguable (samples 2, 9 and 16) and are flagged in their why; in each case the PDF answer is kept. The real exam uses 5 options per question.

Recall

With k = 4 correct options, what do you score for ticking 3 correct and 1 wrong?

(3 x 1/4) - (1 x 1/4) = 3/4 - 1/4 = 1/2.