Practice gce model questions vol1 computer_studies 2025 Past Questions

Question 1 View Details

Company X has identified three security threats with the following likelihoods (per year) and monetary impacts: - Threat A: likelihood $0.03$, impact ₦4,000,000 - Threat B: likelihood $0.04$, impact ₦2,500,000 - Threat C: likelihood $0.02$, impact ₦6,000,000 Risk is calculated as $ \text{Risk} = \text{Likelihood} \times \text{Impact} $. Three possible controls are available: - Control X reduces likelihood by 40 % (i.e., multiplies likelihood by 0.6) and costs ₦500,000. - Control Y reduces impact by 30 % (i.e., multiplies impact by 0.7) and costs ₦300,000. - Control Z reduces both likelihood and impact by 20 % (multiplies each by 0.8) and costs ₦600,000. The acceptable residual risk threshold is ₦80,000. Which control should be implemented to bring the highest‑risk threat's residual risk below the threshold at the lowest cost? State the control name.

Correct A. Control X

B. Control Z

C. Control Y

D. Control W

Correct Answer: A

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Question 2 View Details

In a spreadsheet, the unit price of a product is stored in cell $C2$ as ₦150. The table records monthly units sold in column $B$ (rows 5 to 8). The discount rate in column $D$ is determined by the units sold: - If units sold $\ge 500$ → 10 % - If units sold $\ge 300$ but < 500 → 5 % - Otherwise → 0 % Final revenue for each month is calculated as $ \text{Units Sold} \times \text{Unit Price} \times (1 - \text{Discount Rate}) $. Write the formula that should be entered in cell $E5$ for the month of June (where $B5 = 420$) using absolute reference for the unit price and a nested IF to obtain the discount rate, and state the resulting revenue for June.

A. =B5*$C$2*(1-IF(B5>=500,0.10,IF(B5>=300,0.04,0))) ; 60,480

B. =B5*$C$2*(1-IF(B5>=500,0.10,IF(B5>=300,0.10,0))) ; 56,700

C. =B5*$C$2*1-IF(B5>=500,0.10,IF(B5>=300,0.05,0)) ; 62,950

Correct D. =B5*$C$2*(1-IF(B5>=500,0.10,IF(B5>=300,0.05,0))) ; 59,850

Correct Answer: D

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Question 3 View Details

The following pseudocode searches for a target value in an array. ``` 1. SET i = 1 2. WHILE i <= n DO 3. IF array[i] = target THEN 4. PRINT "Found at position", i 5. EXIT LOOP 6. ENDIF 7. i = i + 1 8. ENDWHILE 9. IF i > n THEN 10. PRINT "Not found" 11. ENDIF ``` Assuming the array is indexed from 0 to $n-1$ (as in most programming languages), identify the off‑by‑one error and provide the corrected line(s) of code.

Correct A. SET i = 0 ; WHILE i < n DO

B. SET i = 0 ; WHILE i <= n DO

C. SET i = 1 ; WHILE i < n DO

D. SET i = 1 ; WHILE i <= n DO

Correct Answer: A

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Question 4 View Details

Consider a relation $R(A,B,C,D,E)$ with the functional dependencies: $A \rightarrow B$ $A \rightarrow C$ $C \rightarrow D$ $BC \rightarrow E$ a) Determine the highest normal form of $R$. b) Decompose $R$ into a set of relations that are in Boyce‑Codd Normal Form (BCNF). c) Write an SQL query that returns all values of $A$ for which the corresponding $D$ is greater than 5000 and the corresponding $E$ is less than 2000. Assume the BCNF relations are stored as tables $R1(C,D)$, $R3(B,C,E)$ and $R4(A,B,C)$. d) Given the following data in the three tables: $R1$: $(C=1,D=6000), (C=2,D=4000), (C=3,D=8000), (C=4,D=3000)$ $R3$: $(B=10,C=1,E=1500), (B=11,C=2,E=2500), (B=12,C=3,E=1800), (B=13,C=4,E=2100)$ $R4$: $(A=100,B=10,C=1), (A=101,B=11,C=2), (A=102,B=12,C=3), (A=103,B=13,C=4)$ How many rows will the query return?

Correct A. 2

B. 4

C. 3

D. 1

Correct Answer: A

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Question 5 View Details

An organisation currently stores user passwords using SHA‑256 hashes with a 16‑byte random salt. For each of its 50,000 users, the stored data consists of a 32‑byte hash and a 16‑byte salt. The organisation plans to migrate to Argon2id, which requires a 32‑byte salt and stores a 64‑byte hash. Calculate the additional storage required for the password table after the migration, expressed in megabytes (MB) to two decimal places (1 MB = 1,048,576 bytes).

A. 2.40

Correct B. 2.29

C. 4.58

D. 1.53

Correct Answer: B

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Question 6 View Details

An exam recorded the marks of 60 students in the following grouped table: Score (out of 100) | Number of students 0\u201339 | 5 40\u201349 | 8 50\u201359 | 12 60\u201369 | 15 70\u201379 | 12 80\u201389 | 5 90\u2013100 | 3 (a) Estimate the mean mark using the class mid‑point method. (b) Assuming marks are uniformly distributed within each interval, estimate the percentage of students who passed, given a pass mark of 55. Give the pass percentage rounded to the nearest whole number.

A. 60

Correct B. 66

C. 72

D. 68

Correct Answer: B

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Question 7 View Details

The first computer to implement the stored‑program concept was completed in 1945. The first commercially available computer was released in 1951. How many years elapsed between these two milestones?

A. 7

Correct B. 6

C. 8

D. 5

Correct Answer: B

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Question 8 View Details

A small office has 8 computers. - In a star topology each computer is linked directly to a central hub located at the centre of the office. The cable length from each computer to the hub is 12 m. - In a bus topology the computers are connected along a single linear cable that runs the length of the office; the total length of the bus cable required is 84 m. Because of signal attenuation a repeater must be installed after every 30 m of cable. Each repeater costs ₦1500 and cable costs ₦250 per metre. The hub for the star topology costs ₦8000. Calculate the total cost (cable plus equipment) for each topology and state which topology is cheaper. Answer with the word "star" or "bus".

A. star

B. ring

C. mesh

Correct D. bus

Correct Answer: D

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Question 9 View Details

The first laptop computer was introduced in 1981 and the first tablet computer was introduced in 2010. How many years later was the tablet introduced?

A. 30

B. 31

Correct C. 29

D. 28

Correct Answer: C

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Question 10 View Details

A school uses a spreadsheet to calculate each pupil's final grade before merging the results into a word‑processing document. The spreadsheet contains the following columns (all scores are out of 100): Test 1, Test 2, Assignment, Project, Extra Credit. The final numeric grade is computed as \[\text{Final}=0.2\times\text{Test1}+0.2\times\text{Test2}+0.1\times\text{Assignment}+0.3\times\text{Project}+5+\text{Extra Credit}.\] If the computed grade exceeds 100 it is capped at 100. The data for five students are: \[\begin{array}{lccccc} \text{Student}&\text{Test1}&\text{Test2}&\text{Assignment}&\text{Project}&\text{Extra Credit}\\\hline A&85&90&78&88&10\\ B&95&92&88&94&20\\ C&70&75&80&85&5\\ D&88&87&90&92&15\\ E&100&98&95&97&25 \end{array}\] How many students will have their final grade capped at 100? Provide the number as an integer.

A. 0

B. 3

C. 2

Correct D. 1

Correct Answer: D

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Question 11 View Details

A file of size $12.5\text{ MB}$ is to be transmitted using a stop‑and‑wait protocol over two serial links in series. The first link has a bandwidth of $5\text{ Mbps}$ and a latency of $20\text{ ms}$; the second link has a bandwidth of $2\text{ Mbps}$ and a latency of $50\text{ ms}$. Each data packet carries $1500$ bytes of payload (ignore headers) and acknowledgements are negligible in size. Assuming the sender must wait for an acknowledgement before sending the next packet, calculate the total time required to send the entire file, giving your answer in minutes to one decimal place.

A. 22.1 minutes (approximately)

B. 25.0 minutes (approximately)

Correct C. 20.6 minutes (approximately)

D. 18.4 minutes (approximately)

Correct Answer: C

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Question 12 View Details

Consider a relation $R(A,B,C,D)$ with functional dependencies $A \rightarrow B$, $BC \rightarrow D$ and $D \rightarrow A$.\n(a) State the highest normal form that $R$ satisfies.\n(b) Decompose $R$ into a set of relations that are in Boyce‑Codd Normal Form (BCNF).\n(c) How many relations result from this BCNF decomposition and does the decomposition preserve a lossless join?

Correct A. Highest NF: 1NF; BCNF decomposition yields 3 relations; lossless join is preserved.

B. Highest NF: 1NF; BCNF decomposition yields 2 relations; lossless join is not preserved.

C. Highest NF: 3NF; BCNF decomposition yields 4 relations; lossless join is preserved.

D. Highest NF: 2NF; BCNF decomposition yields 2 relations; lossless join is not preserved.

Correct Answer: A

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Question 13 View Details

A symmetric‑key algorithm uses a 128‑bit key. An attacker can test $10^9$ keys per second.\n(a) How many seconds, on average, would it take to brute‑force half of the key space?\n(b) Convert this time to years (use $1$ year = $3.15576\times10^{7}$ seconds).\n(c) If a security policy requires a minimum resistance of 5 years, does the 128‑bit key meet the requirement?

A. No; the key provides about \\\$5.4\\\times10^{21}\\$ seconds of resistance, which is far below 5 years.

B. Yes; the key provides about \\\$5.4\\\times10^{19}\\$ years of resistance, above 5 years but far less than claimed.

C. No; the key provides only \\\$5.4\\\times10^{3}\\$ years of resistance, which is below the requirement.

Correct D. Yes; the key provides about $5.4\times10^{21}$ years of resistance, far above 5 years.

Correct Answer: D

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Question 14 View Details

A text file contains $100{,}000$ characters, each drawn from an alphabet of 64 symbols. Using Huffman coding the average code length achieved is $5.2$ bits per symbol.\n(a) What is the compression ratio compared with a fixed‑length 6‑bit encoding?\n(b) What percentage reduction in file size does this represent?\n(c) Does the compression meet a target of at least a 12% reduction?

A. Compression ratio ≈ 1.05; reduction ≈ -5.0%; target not met.

B. Compression ratio ≈ 0.80; reduction ≈ 20.0%; target met.

C. Compression ratio ≈ 0.92; reduction ≈ 8.0%; target not met.

Correct D. Compression ratio ≈ 0.87; reduction ≈ 13.3%; target met.

Correct Answer: D

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Question 15 View Details

In which year was the Intel 4004, the first commercially successful microprocessor, released?

Correct A. 1971

B. 1972

C. 1970

D. 1974

Correct Answer: A

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Question 16 View Details

A desktop computer uses a 500 W power‑supply unit. The CPU consumes 95 W, the hard‑disk drive 10 W and the monitor 30 W. The remaining components together use 20 % of the power‑supply's rated capacity. Is the power‑supply sufficient for this system?

Correct A. Yes, the power‑supply is sufficient (total consumption 235 W < 500 W).

B. No, the power‑supply is not sufficient (total consumption 235 W > 500 W).

C. Yes, the power‑supply is sufficient (total consumption 530 W < 500 W).

D. No, the power‑supply is not sufficient (total consumption 530 W > 500 W).

Correct Answer: A

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Question 17 View Details

In a small office network that uses a star topology, eight computers are each linked to a central switch with CAT6 cables that support 1 Gbps. Computer A must send a 500 MB file to computer B. The switch adds a processing delay of 0.5 ms for every Ethernet frame, and the Ethernet frame size is 1500 bytes. Assuming the link is fully utilised and ignoring other overheads, estimate the total time required to transfer the file (in seconds).

A. Approximately 175 seconds (≈ 3 min 5 s).

B. Approximately 200 seconds (≈ 3 min 20 s).

C. Approximately 150 seconds (≈ 2 min 30 s).

Correct D. Approximately 175 seconds (≈ 2 min 55 s).

Correct Answer: D

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Question 18 View Details

A processor has a 32‑bit address bus. How many bytes of memory can it address?

A. 2 GB

Correct B. 4 GB

C. 8 GB

D. 16 GB

Correct Answer: B

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Question 19 View Details

A program sorts an array of 10 000 integers using bubble sort. In the worst case bubble sort makes $\frac{n(n-1)}{2}$ comparisons, each taking 0.2 µs. The same array is then sorted with merge sort, which requires about $n\log_{2}n$ comparisons, each taking 0.05 µs. Calculate the time taken by each algorithm (in seconds) and the time saved by using merge sort.

A. Bubble sort ≈ 12 s; merge sort ≈ 0.008 s; time saved ≈ 11.99 s.

B. Bubble sort ≈ 9 s; merge sort ≈ 0.005 s; time saved ≈ 8.99 s.

Correct C. Bubble sort ≈ 10 s; merge sort ≈ 0.0066 s; time saved ≈ 9.99 s.

D. Bubble sort ≈ 15 s; merge sort ≈ 0.010 s; time saved ≈ 14.99 s.

Correct Answer: C

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Question 20 View Details

An organisation has been allocated the address block 192.168.64.0/20. It needs subnets for three departments: Administration (≥ 200 hosts), Research (≥ 500 hosts) and Development (≥ 1 000 hosts). Propose a subnetting scheme that satisfies each department's minimum host requirement using the smallest possible subnet mask for each, and give the network address and mask for each subnet.

A. Development: 192.168.64.0/22; Research: 192.168.68.0/24; Administration: 192.168.69.0/24.

Correct B. Development: 192.168.64.0/22; Research: 192.168.68.0/23; Administration: 192.168.70.0/24.

C. Development: 192.168.64.0/21; Research: 192.168.72.0/23; Administration: 192.168.74.0/24.

D. Development: 192.168.64.0/22; Research: 192.168.68.0/23; Administration: 192.168.70.0/25.

Correct Answer: B

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Question 21 View Details

A database contains three tables. Table A has 150\,000 records with an average record size of 120\,bytes, Table B has 80\,000 records with an average size of 200\,bytes, and Table C has 50\,000 records with an average size of 350\,bytes. A new indexing scheme reduces the average record size of Tables A and B by 12\% but increases the average size of Table C by 5\% because of additional index overhead. What is the overall percentage change in the total size of the database after applying the scheme? Give your answer to one decimal place and state whether it is an increase or a reduction.

A. 5.8% reduction

B. 6.2% increase

Correct C. 6.2% reduction

D. 7.0% reduction

Correct Answer: C

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Question 22 View Details

A school's computer network is built as follows. The computer lab uses a star topology with 10 computers, each connected to a central switch by a 5\,m cable. The administration office uses a bus topology with 8 computers linked linearly; the distance between each adjacent pair of computers is 6\,m. The two subnetworks are joined by a single 30\,m Ethernet cable. The cost of cable is $2 per metre for the star links, $1.5 per metre for the bus links, and $3 per metre for the linking cable. (a) What is the total cost of the cabling for the whole network? (b) If a redundant 30\,m link is added between the switch and the administration office at the same cost per metre, what is the percentage increase in the total cabling cost? Give your answer to one decimal place.

Correct A. 35.6% increase

B. 34.2% increase

C. 36.8% increase

D. 35.6% reduction

Correct Answer: A

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Question 23 View Details

An organisation evaluates three security threats. Threat A has a probability of occurrence of 0.02 per year and would cause a loss of $250,000. Threat B has a probability of 0.05 per year and a loss of $120,000. Threat C has a probability of 0.01 per year and a loss of $500,000. The organisation can install a security control that reduces the probability of Threat A by 60\% and the probability of Threat C by 40\%, at an annual cost of $30,000. The control does not affect Threat B. Using the criterion that the expected annual loss reduction must exceed the cost of the control, should the control be implemented? Show your calculations.

A. Yes, because the expected loss reduction $5,000 exceeds the control cost $30,000.

Correct B. No, because the expected loss reduction $5,000 is less than the control cost $30,000.

C. No, because the expected loss reduction $5,000 is greater than the control cost $30,000.

D. No, because the expected loss reduction $35,000 is less than the control cost $30,000.

Correct Answer: B

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Question 24 View Details

A web page contains a parent container of fixed width 1200\,px. Inside it is a div with the following CSS: width = 80\%; padding = 20\,px (all sides); border = 5\,px (all sides); margin = 10\,px (all sides). An image placed inside the div has an intrinsic width of 800\,px and the rule max‑width: 100\%; height: auto. (a) What is the displayed width of the image in pixels when the page is viewed on a screen where the parent width remains 1200\,px? (b) A media query changes the div's width to 60\% for screens narrower than 800\,px. If the parent container is then 600\,px wide, what is the displayed image width? Give your answers in pixels.

A. 720 px and 360 px

B. 800 px and 420 px

C. 800 px and 300 px

Correct D. 800 px and 360 px

Correct Answer: D

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Question 25 View Details

Consider a relation R(A, B, C, D) with the functional dependencies A → B, B → C and C → D. The domain sizes are |A| = 30, |B| = 30, |C| = 30 and |D| = 30, and the relation currently holds 1200 tuples, assumed to be uniformly distributed. (a) State the highest normal form that R satisfies. (b) Decompose R into a set of BCNF relations. (c) Assuming the decomposition is lossless‑join and that duplicate tuples are eliminated in each resulting relation, estimate the total number of tuples across all BCNF relations after decomposition.

A. 240 tuples

B. 150 tuples

Correct C. 90 tuples

D. 180 tuples

Correct Answer: C

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