S6 ICT Practice Paper | Number Systems, File Size, SQL, Algorithm Complexity, Subnetting And Security (with Answers)

S6 ICT Practice Paper | Number Systems, File Size, SQL, Algorithm Complexity, Subnetting and Security (with answers)

2026-11-15

ICT – Secondary 6

S6 ICT practice paper: number systems, file size, SQL, algorithm tracing, subnetting and security. Six questions, 100 marks, 60 minutes, with full answers.

Paper details　

Question 1: Data representation and number systems

Show your working for every part.

#	Question	Answer and marking notes
1	Convert hexadecimal D7 to decimal and write its binary representation.	Answer: D7 = 13 x 16 + 7 = 215; its binary form is 11010111.
2	An uncompressed bitmap is 1920 x 1080 pixels with 24-bit colour. Find its file size (1 MB = 1,048,576 bytes, 2 decimal places).	Answer: 1920 x 1080 x 24 / 8 = 6,220,800 bytes; / 1,048,576 = 5.93 MB.
3	Uncompressed audio is sampled at 44.1 kHz, 16-bit, stereo, lasting 180 s. Find its file size (1 MB = 1,048,576 bytes, 2 decimal places).	Answer: 44,100 x 16 x 2 x 180 / 8 = 31,752,000 bytes; / 1,048,576 = 30.28 MB.
4	Explain lossless compression and lossy compression, giving one example of each.	Answer: Lossless compression restores the original data exactly, e.g. ZIP; lossy compression discards some data for a smaller file, e.g. JPEG.

Question 2: Relational databases and SQL

The table STUDENT (SID, SNAME, CLASS, SCORE) stores student ID, name, class and score.

#	Question	Answer and marking notes
5	Explain the roles of a primary key and a foreign key, and state which column of STUDENT is suitable as the primary key.	Answer: A primary key uniquely identifies each row and cannot repeat or be empty; a foreign key references the primary key of another table to form a relationship. SID is suitable as the primary key.
6	Write SQL to list the classes whose average score is above 70 together with the average, and state the result.	Answer: SELECT CLASS, AVG(SCORE) FROM STUDENT GROUP BY CLASS HAVING AVG(SCORE) > 70; the result is 6A average 81.5; 6C average 78.5.
7	Write SQL to find the name and score of the top-scoring student, and state the result.	Answer: SELECT SNAME, SCORE FROM STUDENT ORDER BY SCORE DESC LIMIT 1; the result is WONG Chi Keung with 91 marks.
8	A student may join several clubs and a club has many students. Explain how to design the tables to avoid duplicated data.	Answer: Add two tables: CLUB (CLUB_ID, CNAME, FEE) and STUDENT_CLUB (SID, CLUB_ID, JOIN_DATE), using the pair SID and CLUB_ID as the composite primary key so each club is stored only once.

Question 3: Algorithms and programming

The Python code is: def f(n): total = 0; for i in range(1, n + 1): if i % 3 == 0: total = total + i; return total

#	Question	Answer and marking notes
9	Trace the code, state the output of f(20) and list the values added together.	Answer: The values added are 3, 6, 9, 12, 15 and 18, so the output is 63.
10	Rewrite the for loop as a while loop so that the output stays unchanged (write the full code).	Answer: total = 0; i = 1; while i is at most 20: if i mod 3 equals 0 then total = total + i; i = i + 1; finally return total, which still gives 63.
11	State the time complexity of the function and explain your answer.	Answer: O(n). The loop runs from 1 to n, n iterations in total, and each iteration does constant-time work, so the running time grows linearly with n.
12	Using binary search on 1,048,576 sorted items, what is the maximum number of comparisons? Explain why binary search cannot be used on unsorted data.	Answer: 2 to the power 20 equals 1,048,576, so at most 20 comparisons are needed. With unsorted data we cannot tell which half holds the target, so the search interval cannot be halved.

Question 4: Computer networks and communication

A department uses the network 192.168.10.0/26.

#	Question	Answer and marking notes
13	For host 192.168.10.70/26, state the network address and the broadcast address of its subnet.	Answer: Each subnet has 64 addresses and 70 falls within 64 to 127, so the network address is 192.168.10.64 and the broadcast address is 192.168.10.127.
14	How many usable host addresses does the subnet provide? Show the calculation.	Answer: There are 32 – 26 = 6 host bits, so 2 to the power 6 gives 64 addresses; after removing the network and broadcast addresses, 62 remain usable.
15	Compare TCP and UDP, giving one application example for each.	Answer: TCP is connection-oriented, reliable and ordered, e.g. HTTP web browsing; UDP is connectionless, does not guarantee delivery but has low overhead, e.g. live streaming or DNS queries.
16	Outline the main steps from typing a URL to the browser displaying the page.	Answer: DNS resolves the domain name to an IP address, a TCP connection is opened with a TLS handshake, an HTTP request is sent, the server responds, and the browser parses HTML, CSS and JavaScript to render the page.

Question 5: Information systems and system development

Short-answer question: keep answers concise and use correct terminology.

#	Question	Answer and marking notes
17	List the five main stages of the system development life cycle (SDLC).	Answer: Feasibility study and requirements analysis, system design, programming and construction, testing, implementation and maintenance.
18	Explain unit testing, integration testing and acceptance testing.	Answer: Unit testing checks a single component; integration testing checks the interfaces and data passing between components; acceptance testing lets users confirm the system meets business needs.
19	Compare file-based processing with a database system, giving one advantage of each.	Answer: File-based processing is simple and cheap to set up, suiting small single-purpose tasks; a database reduces data duplication and supports shared multi-user access with consistency control.
20	Explain how SaaS, PaaS and IaaS differ, with one example of each.	Answer: SaaS delivers a ready application, e.g. webmail; PaaS provides a development and runtime platform, e.g. a cloud app hosting service; IaaS supplies raw resources such as virtual machines and storage, e.g. a cloud virtual server.

Question 6: Information security and social issues

Short-answer question: keep answers concise and use correct terminology.

#	Question	Answer and marking notes
21	Compare symmetric and asymmetric encryption and explain why HTTPS uses both.	Answer: Symmetric encryption uses one shared key, which is fast but hard to distribute securely; asymmetric encryption uses a public and a private key, which is safe for key exchange but slower. HTTPS exchanges a symmetric key asymmetrically, then encrypts bulk data symmetrically.
22	Describe phishing and ransomware, giving one defence measure for each.	Answer: Phishing uses fake messages to steal accounts or personal data; defence is to verify the sender domain and avoid suspicious links. Ransomware encrypts files and demands payment; defence is offline backup plus timely patching.
23	Discuss how open-source and proprietary licences differ on modification and redistribution.	Answer: An open-source licence allows access to the source code, modification and redistribution under its terms; a proprietary licence grants use only and normally forbids modification and redistribution.
24	A password has 8 characters, each being one of 26 uppercase letters or 10 digits. Find the total number of combinations and explain why increasing length is usually more effective than adding character types.	Answer: 36 to the power 8 equals 2,821,109,907,456 combinations. Each extra character multiplies the count by 36, far more than slightly widening the character set, so a longer password resists brute force better.

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