A student's program that averages three test scores runs without any error message, but it always reports an average that is too high. The code adds the three scores and divides by 2 instead of 3. What kind of error is this?
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About this test
This is a free 15-question sampler in the style of the AP Computer Science Principles multiple-choice section, written by the StudyPDF team from the five Big Ideas the College Board publishes for the course. It covers creative development, data, algorithms and programming in exam-style pseudocode, computer systems and networks, and the impact of computing, in roughly the weights the exam uses. You will meet multiple choice, select all that apply and fill in the blank. Answer all 15, then check your score and read the explanation for every question.
All 15 questions at a glance
Prefer to read before you play? Every question in the sampler is listed below. Answers and explanations stay collapsed until you open them.
1.A student's program that averages three test scores runs without any error message, but it always reports an average that is too high. The code adds the three scores and divides by 2 instead of 3. What kind of error is this?
- A. Syntax error
- B. Logic error
- C. Overflow error
- D. Run-time error
Answer: B. Logic error
A logic error is a mistake in the algorithm: the program runs and produces a result, but the result is wrong. A syntax error breaks the rules of the language, so the program will not run at all. A run-time error stops the program while it is running, for example by dividing by zero, and an overflow error happens when a value is too large for the number of bits the computer uses to store it. Logic errors are the hardest to find because nothing crashes, which is why testing with inputs whose answer you already know matters.
2.Which practices are part of an iterative, collaborative way to develop a program?
Select all that apply.
- A. Building a small working version, testing it with users and revising it
- B. Having teammates review each other's code to catch errors and bring different perspectives
- C. Writing the whole program before running it even once, so nothing half-finished confuses the team
- D. Writing comments and documentation that explain what a code segment is for
- E. Keeping the design secret from users until the final version is done
Answer: A. Building a small working version, testing it with users and revising it, B. Having teammates review each other's code to catch errors and bring different perspectives, D. Writing comments and documentation that explain what a code segment is for
Iterative development means building, testing and refining in small steps, so mistakes show up early and feedback shapes the next version. Collaboration brings in other viewpoints, and people with different backgrounds notice different problems and needs. Documentation helps teammates, and your future self, understand what code was meant to do. Writing everything before the first run lets errors pile up, and hiding the design from users removes the feedback the process depends on.
3.Complete the sentence.
In binary, the number 1011 equals _____ in decimal, and a sequence of 8 bits can represent _____ different values.
Options for blank 1: 9, 11, 13, 15
Options for blank 2: 16, 128, 255, 256
Answer: 11, 256
Each binary place is worth twice the one to its right: 8, 4, 2, 1. So 1011 is 8 + 0 + 2 + 1 = 11. With n bits there are 2 to the power n different patterns, and 2^8 = 256, so 8 bits can represent 256 different values, from 0 through 255. The 255 option is the largest number that fits in 8 bits, not the count of values, and that off-by-one is a classic trap.
4.A museum is compressing scans of old documents and must be able to rebuild every original pixel exactly. Which approach should it use?
- A. Lossless compression
- B. Lossy compression with the quality set to high
- C. Lossy compression after deleting every second row of pixels
- D. Any compression, since a rebuilt file always matches the original
Answer: A. Lossless compression
Lossless compression reduces file size in a way that lets the original data be reconstructed exactly, which is what an archive needs. Lossy compression gets smaller files by throwing information away for good, and even at high quality the original cannot be rebuilt. Lossy is a sensible trade for streaming video or casual photos, where small differences are hard to see. The cost of lossless is that files stay larger.
5.A phone photo file includes the date, the GPS location and the camera model along with the image itself. Which statement is correct?
- A. Metadata is the part of the image that is lost when the photo is compressed
- B. Metadata can only be created by the person who views the file
- C. Metadata changes the pixels of the image every time the photo is copied
- D. Metadata is data about other data, and it can reveal private details even if you only share the photo
Answer: D. Metadata is data about other data, and it can reveal private details even if you only share the photo
Metadata describes a piece of data without being the data itself: when a photo was taken, where, with what device. It helps people organize and search large collections, and it can be changed or deleted without changing the image. It can also expose things the sender never meant to share, such as a home location, so many apps remove it on upload. Metadata is not lost by compression and does not alter the pixels.
6.total ← 0. FOR EACH item IN [3, 8, 12, 5, 10], IF (item MOD 2 = 0), then total ← total + item. After the loop, DISPLAY(total). What is displayed?
- A. 8
- B. 10
- C. 30
- D. 38
Answer: C. 30
item MOD 2 is the remainder when item is divided by 2, so the test is true only for even numbers. The even items are 8, 12 and 10, and 8 + 12 + 10 = 30. The 38 answer adds every item, as if the test were missing, and 8 is the sum of the odd items, 3 + 5. When you trace a loop, write the value of total after each pass, so the one skipped odd number is easy to see.
7.nums ← [4, 8, 15, 16]. Then INSERT(nums, 2, 23), REMOVE(nums, 1) and APPEND(nums, 42) run in that order. List positions start at 1. What does DISPLAY(nums[3]) show?
- A. 8
- B. 15
- C. 16
- D. 23
Answer: B. 15
Trace the list after each step. Start with [4, 8, 15, 16]. INSERT at position 2 puts 23 there and shifts the rest right: [4, 23, 8, 15, 16]. REMOVE position 1 deletes the 4: [23, 8, 15, 16]. APPEND adds 42 at the end: [23, 8, 15, 16, 42]. Position 3 holds 15. The 8 answer comes from forgetting that INSERT shifts items, and 16 comes from counting positions from 0 instead of 1.
8.Complete the sentence.
Suppose p is true and q is false. Then p AND (NOT q) evaluates to _____, and NOT (p OR q) evaluates to _____.
Options for blank 1: true, false
Options for blank 2: true, false
Answer: true, false
Work from the inside out. NOT q is true because q is false, so p AND (NOT q) is true AND true, which is true. For the second one, p OR q is true OR false, which is true, and NOT true is false. AND is true only when both sides are true, OR is true when at least one side is, and NOT flips the value. Writing each sub-result on its own line prevents most mistakes.
9.Which statements about algorithms are true?
Select all that apply.
- A. Every algorithm can be built from sequencing, selection and iteration
- B. A faster computer can make any undecidable problem solvable
- C. Two different algorithms can solve the same problem while using very different numbers of steps
- D. A heuristic can be used when finding the best solution would take an unreasonable amount of time
- E. An algorithm whose steps double with every added input is the best choice for very large inputs
Answer: A. Every algorithm can be built from sequencing, selection and iteration, C. Two different algorithms can solve the same problem while using very different numbers of steps, D. A heuristic can be used when finding the best solution would take an unreasonable amount of time
Sequencing, selection and iteration are enough to express any algorithm. Different algorithms for one problem can differ hugely in efficiency, which is why comparing step counts matters. A heuristic gives a good-enough answer in reasonable time when the exact answer is out of reach. An undecidable problem has no algorithm that works for every input, however fast the machine, and a step count that doubles with each added input quickly becomes unusable, since it is not a reasonable-time algorithm.
10.A city engineer uses a computer simulation of rush-hour traffic to test new traffic light timing before changing the real intersection. Which statement about the simulation is accurate?
- A. It is always more reliable than watching the real intersection, because a simulation never leaves anything out
- B. It cannot be used until the real intersection has been rebuilt
- C. It removes the need for any data about real traffic
- D. It lets the city test changes without cost or risk, but the results depend on what the model left out
Answer: D. It lets the city test changes without cost or risk, but the results depend on what the model left out
A simulation is an abstraction: it keeps the details that matter for the question and leaves the rest out. That makes it cheap and safe to try ideas, such as many timings in an afternoon, which would be impractical on a real street. The limit is that the results are only as good as the model and the data behind it, so a factor left out, such as a road closure, can make the real outcome differ. That is why simulation results are checked against real observations.
11.A school network connects each building to at least two others, so students can still reach the Internet if one cable is cut. Which statement best describes this design?
- A. It is fault tolerant, because redundant paths keep the network working after a failure
- B. It has higher bandwidth, because each cable carries more data
- C. It has lower latency, because messages always take the shortest path
- D. It is encrypted, because messages cannot be read in transit
Answer: A. It is fault tolerant, because redundant paths keep the network working after a failure
The Internet is built to be fault tolerant: there are usually several paths between two points, so routing can send data around a broken link. Extra connections do not by themselves raise bandwidth, which is how much data can move per second, and an alternate path can even be longer. Encryption is about privacy, not about surviving a failure. Redundancy is the key word for this kind of question.
12.Complete the sentence.
The Domain Name System (DNS) looks up a _____ such as example.org and returns the matching _____, which routers use to deliver packets.
Options for blank 1: packet, domain name, protocol, password
Options for blank 2: IP address, bit rate, file format, encryption key
Answer: domain name, IP address
People use names such as example.org because they are easy to remember, but routers move data by IP address. DNS is the lookup service that translates a domain name into the IP address of the server. Without it you would have to type numbers to visit a site. A packet is a small chunk of data that travels the Internet, and a protocol is an agreed set of rules, such as TCP and IP.
13.A company trains a program to screen job applications using the records of people it hired over the past 20 years, most of whom came from a few similar backgrounds. Which concern is most likely?
- A. The program will be fair, because computers cannot have bias
- B. The program cannot run, because applications are not binary data
- C. The program may repeat the pattern in the old hiring data, which is a form of computing bias
- D. The program will only improve if the old records are deleted after training
Answer: C. The program may repeat the pattern in the old hiring data, which is a form of computing bias
Computing bias can come from the data a program learns from or from choices its designers make. A model trained on past decisions can copy their patterns, including unfair ones, and it can do so at scale and with an air of objectivity. Computers do not make bias impossible, and all digital data, including text, is stored in binary. Reducing bias takes steps such as checking results across groups and using more representative data, not deleting records.
14.Which actions help protect an online account from being taken over?
Select all that apply.
- A. Turning on multifactor authentication
- B. Reusing one strong password on every site so it is easy to remember
- C. Treating a message that asks you to log in through a link with suspicion, since phishing tries to trick you into giving up your login
- D. Using a different, long password for each account, ideally with a password manager
- E. Sharing the one-time login code with anyone who says they work for support
Answer: A. Turning on multifactor authentication, C. Treating a message that asks you to log in through a link with suspicion, since phishing tries to trick you into giving up your login, D. Using a different, long password for each account, ideally with a password manager
Multifactor authentication requires a second proof besides the password, so a stolen password alone is not enough. Phishing is an attempt to trick people into entering credentials on a fake page, so going to the site directly beats clicking a link in a message. Unique passwords limit the damage if one site is breached, and a password manager makes them practical. Reusing a password lets one breach open many accounts, and a one-time code is meant for you alone, so no legitimate support team asks for it.
15.Maria publishes her public key. Devon wants to send her a message that only she can read, using public-key encryption. Which key does Devon use to encrypt it?
- A. Devon's private key
- B. Devon's public key
- C. Maria's private key
- D. Maria's public key
Answer: D. Maria's public key
In public-key encryption each person has a pair of keys. Anyone can use Maria's public key to encrypt a message to her, but only her private key can decrypt it, so only she can read it. Devon's own keys are not involved in this direction. The private key must never be shared, which is the whole point of the pair. Public keys are what let a browser start a secure connection with a site it has never met.
What the AP CSP exam looks like and how the Big Ideas are weighted
The AP Computer Science Principles exam is scored 1 to 5 and has two parts. According to the College Board, the end-of-course exam is fully digital in the Bluebook app. Section I is 70 multiple-choice questions in 120 minutes and counts for 70 percent of your score, with four answer options each: 57 are single-select, 5 are single-select questions built on a reading passage about a computing innovation, and 8 are multiple-select questions where you choose 2 answers. Section II counts for the other 30 percent. It combines the Create performance task with 2 written-response questions, 4 prompts in all, that you answer in a 60-minute part of the exam day and that ask about your own program.
The College Board splits the course into five Big Ideas and publishes how much of the exam score each one gets. Algorithms and programming is the heaviest at 30 to 35 percent. Impact of computing is 21 to 26 percent, data is 17 to 22 percent, computer systems and networks is 11 to 15 percent, and creative development is 10 to 13 percent. So about a third of the exam is algorithms and programming, much of it reading and tracing code, and about a quarter is the impact of computing on people, which is the part students most often leave until last.
The College Board lists the 2027 exam for Friday, May 14, in Session 1, and the Create performance task is due as final in the AP Digital Portfolio by 11:59 p.m. ET on Friday, April 30. Dates change from year to year, so check the College Board page for your own exam year. What a score earns is up to each college, so look up the policy at the schools you care about.
How to use this sampler, and what it leaves out
The 15 questions are spread across the Big Ideas in about the same proportions as the exam: five on algorithms and programming, three on data, three on impact of computing, two on computer systems and networks and two on creative development. They ask for the reasoning behind an answer more than a memorized term: why a program that runs can still be wrong, why lossless compression is the right tool when every pixel matters, why a simulation is useful and still limited, why a model trained on old data can repeat old unfairness.
The coding questions use plain-text pseudocode in the style of the exam. An arrow means assign, so x ← 3 stores 3 in x. Lists start at position 1, not 0, and MOD gives the remainder of a division. The exam uses its own pseudocode, not Python or Java, so you can practice it even if your class works in another language. Take it in one sitting with scratch paper, trace each program by writing down the value of every variable after every line, and then read the explanation for every question, including the ones you got right.
This sampler does not practice the Create performance task. That is the program you build in class over about 9 hours, with the code, a short video of it running and a Personalized Project Reference, and your written responses on exam day are about that same program. Work on it with your teacher and the College Board's student handouts, and treat the questions here as practice for the multiple-choice section only. The questions are original and written to the published course outline. They are not released exam questions.
How StudyPDF builds AP CSP practice tests from your class notes
Fifteen questions can show you which Big Idea is shaky. They cannot get you ready on their own, and a generic bank rarely matches the vocabulary, the examples and the pseudocode your teacher actually uses.
StudyPDF works from your material instead. Upload your class notes, your teacher's slides, a worked problem set or your review packet, press New material, and StudyPDF builds practice tests from those exact pages. Every question is grounded in your material and every explanation cites where the answer comes from, so you can go straight back to the page when a step does not make sense.
You do not need to upload anything to start. Name a topic instead, for example the Internet and DNS, or lists and iteration, and Bo sets it up with its key concepts so you can build quizzes and flashcards on it. Your results track which concepts you keep missing, so the next practice test can target them. Starting is free.
Written by the StudyPDF team. Last updated August 19, 2026.
Good to know
Is this AP Computer Science Principles practice test really free?
Yes. All 15 questions, the score screen and every explanation are free to play in your browser, and there is no paywall on this page.
How is the AP CSP exam structured?
According to the College Board, Section I is 70 multiple-choice questions in 120 minutes and counts for 70 percent of your score. Section II counts for 30 percent and combines the Create performance task, which you build in class over about 9 hours, with 2 written-response questions in a 60-minute part of exam day. The exam is taken in the Bluebook app. Check the College Board page for the current exam date.
Who wrote these questions, and do they cover the Create task?
The StudyPDF team wrote every question and explanation from the Big Ideas the College Board publishes for the course. They are not released exam questions and they are not taken from any prep provider's bank. The Create performance task is not practiced here, since it is a program you build yourself. StudyPDF is not affiliated with the College Board, and AP is a trademark of the College Board.
Can I get more questions like these from my own class notes?
Yes. Upload your class notes, slides or review packet to StudyPDF, and Bo builds full-length practice tests from those exact pages, with explanations that cite where each answer came from. If you only have a paper copy, name a topic instead, for example lists and iteration, and Bo writes a test from that.
Need more than a sampler?
Upload your own prep book, slides or notes and Bo builds full-length practice tests from your exact materials, tracks which concepts you keep missing and targets your weak spots. Free to start.