Practice neco data_processing 2025 Past Questions

Question 1 View Details

A spreadsheet column A contains the numbers 45, 78, 62, 91 and 54. What is the sum \(45 + 78 + 62 + 91 + 54\)?

A. 239

B. 276

C. 268

Correct D. 330

Correct Answer: D

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Question 2 View Details

A company enforces a password policy that requires passwords to be exactly 8 characters long, using uppercase letters (26), lowercase letters (26) and digits (10). An attacker attempts a brute‑force attack, trying \(1{,}000{,}000\) random passwords uniformly from all possible passwords that meet the policy. (a) Compute the probability that the attacker guesses a particular strong password within these attempts. (b) In practice, 10\% of users choose simple passwords that effectively reduce the password space to \(10^{6}\) possible passwords, while the remaining 90\% use passwords that fully exploit the policy. Assuming the attacker's attempts are equally likely to target any user, calculate the overall probability that the attacker compromises an account in one attack session. (c) If the organisation considers a policy acceptable only when the overall compromise probability is less than \(0.001\), should the current policy be retained? Justify your answer.

A. (a) \(4.6\times10^{-7}\) (approximately)\n(b) \(0.10\) (10\%)\n(c) No, the policy is not acceptable because the overall compromise probability (0.10) exceeds 0.001.

Correct B. (a) \(4.6\times10^{-9}\) (approximately)\n(b) \(0.10\) (10\%)\n(c) No, the policy is not acceptable because the overall compromise probability (0.10) exceeds 0.001.

C. (a) \(4.6\times10^{-9}\) (approximately)\n(b) \(0.09\) (9\%)\n(c) No, the policy is not acceptable because the overall compromise probability (0.09) exceeds 0.001.

D. (a) \(4.6\times10^{-8}\) (approximately)\n(b) \(0.05\) (5\%)\n(c) Yes, the policy is acceptable because the overall compromise probability (0.05) is less than 0.1.

Correct Answer: B

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Question 3 View Details

A student has a 64 GB USB drive. He stores two types of files: text files (average size \(0.8\) MB) and video files (average size \(700\) MB). After compressing all files with a zip utility, the total storage used becomes \(48\) GB. The compression reduces the size of each text file by \(30\%\) and each video file by \(10\%\). If the number of video files is twice the number of text files, how many video files are stored on the drive?

A. 84

B. 72

C. 90

Correct D. 78

Correct Answer: D

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Question 4 View Details

An organisation identifies three security threats with the following probabilities and monetary impacts per year: - Malware infection: probability \(0.02\), impact \(\text{₦}5{,}000{,}000\). - Insider data theft: probability \(0.005\), impact \(\text{₦}12{,}000{,}000\). - Phishing attack: initial probability \(p_{0}=0.04\), impact \(\text{₦}3{,}000{,}000\). The organisation can invest in employee‑training programmes that halve the phishing probability for each \(\text{₦}500{,}000\) spent, up to a maximum reduction of \(80\%\) (i.e., the probability cannot be reduced below \(0.2p_{0}\)). With a training budget of \(\text{₦}1{,}500{,}000\), determine: (a) The final phishing probability after the training. (b) The expected annual loss (sum of probability × impact for all three threats) after the training. (c) Whether the expected loss is below the acceptable risk threshold of \(\text{₦}200{,}000\).

A. (a) 0.010\n(b) ₦190,000\n(c) No, the expected loss is above the threshold.

B. (a) 0.012\n(b) ₦210,000\n(c) No, the expected loss exceeds the threshold.

C. (a) 0.008\n(b) ₦200,000\n(c) No, the expected loss is not below the threshold.

Correct D. (a) 0.008\n(b) ₦184,000\n(c) Yes, the expected loss is below the threshold.

Correct Answer: D

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Question 5 View Details

A file system uses a fixed block size of \(4{,}096\) bytes. For each file, the system reserves an additional \(128\) bytes for metadata. Consider a file whose actual data size is \(10{,}250\) bytes. (a) How many blocks are allocated to store this file (including metadata)? (b) What is the total amount of disk space, in bytes, occupied by the file? (c) If the disk capacity is \(2\) GB, what percentage of the disk does this file occupy? Express your answer to three significant figures.

A. (a) 2 blocks\n(b) 8,192 bytes\n(c) 0.381%

B. (a) 3 blocks\n(b) 12,288 bytes\n(c) 0.057%

C. (a) 4 blocks\n(b) 16,384 bytes\n(c) 0.763%

Correct D. (a) 3 blocks\n(b) 12,288 bytes\n(c) 0.586%

Correct Answer: D

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Question 6 View Details

School A has 1,200 students, of which \(65\%\) use the internet daily. School B has 800 students, with \(58\%\) daily users. School C has 1,500 students, with \(72\%\) daily users. The Ministry requires the overall proportion of daily internet users to be at least \(68\%\). Determine whether the target is met. If it is not, state whether adding any number of additional students to School B (who would have the same \(58\%\) usage rate) could achieve the target.

A. Target met; the combined proportion of daily internet users already exceeds 68%.

Correct B. Target not met; adding any number of students to School B with the same 58% usage cannot achieve 68%.

C. Target not met; adding students to School B with a 58% usage rate would raise the overall proportion to exactly 68%.

D. Target not met; adding any number of students to School B with the same 58% usage could achieve the 68% target.

Correct Answer: B

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Question 7 View Details

A raw data set contains 500 records. Eight percent of the records are duplicate entries, and five percent have missing values. During data cleaning, duplicate records are removed first, then missing values are imputed with the mean. After cleaning, how many records remain and what is the overall percentage reduction from the original data set?

A. 460 records remain; 5% reduction.

B. 475 records remain; 5% reduction.

C. 435 records remain; 13% reduction.

Correct D. 460 records remain; 8% reduction.

Correct Answer: D

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Question 8 View Details

A student records the minutes spent on homework each day for a week: 45, 50, 55, 40, 60, 35 and 50 minutes. What is the average number of minutes spent on homework per day, correct to one decimal place?

A. 46.4

B. 48.6

Correct C. 47.9

D. 47.8

Correct Answer: C

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Question 9 View Details

In a test of 40 students, the scores are grouped as follows: 0-19: 2 students, 20-39: 5 students, 40-59: 12 students, 60-79: 15 students, 80-100: 6 students. Assuming a uniform distribution of scores within each interval, estimate the median score of the class.

A. 58

B. 66

Correct C. 62

D. 70

Correct Answer: C

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Question 10 View Details

A small business records inventory manually, taking 3 hours each day. They consider buying spreadsheet software that costs \(\text{₦}500,000\) with an annual maintenance fee of \(\text{₦}30,000\). The software reduces recording time to 2 hours per day. Employees are paid \(\text{₦}2,500\) per hour. The software also improves stock accuracy, reducing loss value by 12\% of monthly sales of \(\text{₦}500,000\). The business also depreciates the hardware needed for the software (cost \(\text{₦}120,000\)) straight‑line over 3 years. Assuming 30‑day months, calculate the net monthly benefit after accounting for labor savings, loss reduction, maintenance, and depreciation. Then state the total net benefit over 24 months and whether it exceeds the initial software cost by at least 20\%.

Correct A. Net monthly benefit ≈ ₦129,166.67; total net benefit over 24 months ≈ ₦3,100,000; yes, it exceeds the initial cost by more than 20%.

B. Net monthly benefit ≈ ₦115,000; total net benefit over 24 months ≈ ₦2,760,000; yes, it exceeds the initial cost by more than 20%

C. Net monthly benefit ≈ ₦129,166.67; total net benefit over 24 months ≈ ₦2,500,000; yes, it exceeds the initial cost by exactly 20%

D. Net monthly benefit ≈ ₦140,000; total net benefit over 24 months ≈ ₦3,360,000; no, it does not exceed the initial cost by 20%

Correct Answer: A

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Question 11 View Details

A small retail shop records its daily sales for a week as follows (in naira): 5,200; 4,800; 5,600; 5,100; 5,300; 4,900; and \(x\) for the seventh day. The manager requires that the average daily sales for the week be a whole number and that the median daily sales be \(5,200\). Determine the value of \(x\). Then calculate the percentage increase of the seventh day's sales over the weekly average, giving your answer to two decimal places.

A. x = 5,220; percentage increase ≈ 1.16 %

B. x = 5,213; percentage increase ≈ 1.05 %

Correct C. x = 5,206; percentage increase ≈ 0.93 %

D. x = 5,200; percentage increase ≈ 0.83 %

Correct Answer: C

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Question 12 View Details

The Boolean function \(F(A,B,C,D)\) is defined by the minterms \(\Sigma m(1,3,4,6,9,11,12,14)\).\n(a) Simplify \(F\) to a minimal sum‑of‑products expression using a Karnaugh map.\n(b) Implement the minimal expression using only NAND gates and state the minimum number of NAND gates required.

A. 3

B. 6

C. 5

Correct D. 4

Correct Answer: D

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Question 13 View Details

A class of 120 students took a mathematics test. The distribution of scores is: 30 students scored 70, 45 scored 80, 25 scored 90 and 20 scored 100.\n(a) Find the cumulative frequency for scores less than or equal to 85.\n(b) What percentage of the class scored above 80? Give your answer to one decimal place.

Correct A. Cumulative frequency = 75; Percentage above 80 = 37.5 %

B. Cumulative frequency = 100; Percentage above 80 = 75 %

C. Cumulative frequency = 70; Percentage above 80 = 45.8 %

D. Cumulative frequency = 45; Percentage above 80 = 16.7 %

Correct Answer: A

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Question 14 View Details

An organisation enforces a password policy: each password must be exactly 8 characters long. The allowed characters are uppercase letters (26), lowercase letters (26), digits (10) and symbols (12). A valid password must contain **at least one** character from each of the four categories.\n(a) Using the principle of inclusion-exclusion, calculate the total number of distinct valid passwords.\n(b) If an attacker can test \(10^{9}\) passwords per second, estimate the minimum time required to exhaust the entire password space, expressing the answer in **days**, rounded up to the nearest whole day.

A. 6

Correct B. 5

C. 4

D. 8

Correct Answer: B

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Question 15 View Details

A company maintains a spreadsheet that records quarterly sales (in naira) for three regions. - Region A: Q1 = 12,000; Q2 = 15,000; Q3 = 13,000; Q4 = 16,000\n- Region B: Q1 = 10,000; Q2 = 11,000; Q3 = 11,500; Q4 = 12,000\n- Region C: Q1 = 8,000; Q2 = 9,000; Q3 = 9,500; Q4 = 10,000 Using spreadsheet formulas, answer the following:\n(a) Compute the total annual sales for each region.\n(b) Determine each region's percentage contribution to the overall annual sales, rounded to one decimal place.\n(c) Identify which region experienced the greatest increase in sales from Q1 to Q4.

A. Region B

B. Region D

Correct C. Region A

D. Region C

Correct Answer: C

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Question 16 View Details

Given the Boolean function \(F = \overline{A}B\overline{C} + A\overline{B}C + AB\overline{C} + \overline{A}\overline{B}C\), simplify \(F\) to its minimal sum‑of‑products form.

A. F = B C + \\overline{B}\\overline{C}

B. F = B\\overline{C} + \\overline{A}C

Correct C. F = B\overline{C} + \overline{B}C

D. F = \\overline{B}C + A\\overline{C}

Correct Answer: C

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Question 17 View Details

Thirty students sat for a test. Twelve scored 45 marks, eight scored 60 marks, five scored 72 marks, and the remaining five scored 88 marks. Later the teacher discovers that one of the 88‑mark scores was recorded incorrectly and should have been 78 marks. What is the corrected mean score of the class (express your answer as a mixed number)?

A. 60\frac{2}{3}

B. 59\frac{2}{3}

Correct C. 60\frac{1}{3}

D. 61\frac{1}{3}

Correct Answer: C

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Question 18 View Details

Consider the relation R(StuID, CourseID, Instructor, Grade) with functional dependencies: StuID, CourseID \rightarrow Grade and Instructor \rightarrow CourseID. Determine whether R is in Boyce‑Codd Normal Form (BCNF). If it is not, give a lossless‑join decomposition of R into relations that are in BCNF.

Correct A. R is not in BCNF. Decompose into R1(Instructor, CourseID) and R2(StuID, CourseID, Grade), both in BCNF.

B. R is not in BCNF. Decompose into R1(StuID, Instructor) and R2(CourseID, Grade), both in BCNF.

C. R is in BCNF. No decomposition is needed.

D. R is not in BCNF. Decompose into R1(Instructor, Grade) and R2(StuID, CourseID), both in BCNF.

Correct Answer: A

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Question 19 View Details

Implement the Boolean function \(F = (A + B)\cdot(C + \overline{D})\) using only two‑input NAND gates. What is the minimum number of NAND gates required for a correct implementation?

Correct A. 9

B. 11

C. 10

D. 8

Correct Answer: A

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Question 20 View Details

A computer system uses a three‑level memory hierarchy. Access times and hit ratios are:\n- Cache: 5 ns, hit ratio 0.60\n- Main memory: 70 ns, hit ratio 0.30 of the accesses that miss in cache\n- Secondary storage: 5 ms (5,000,000 ns), accessed only when both cache and main memory miss.\nCalculate the average memory access time (in nanoseconds) for this hierarchy.

A. 500,024 ns

Correct B. 1,400,033 ns

C. 1,400,013 ns

D. 1,400,012 ns

Correct Answer: B

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Question 21 View Details

A student records the exam scores (0\u2013100) of 25 students. Each score is stored as an 8‑bit unsigned integer. Each student's 4‑digit ID number is stored as a 16‑bit unsigned integer. Assuming no other overhead, what is the total size of the file in kilobytes (KB), rounded to two decimal places?

Correct A. 0.07

B. 0.59

C. 0.08

D. 0.60

Correct Answer: A

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Question 22 View Details

A database holds 10,000 employee records, each 120\,bytes long. The file uses indexed‑sequential organization with a primary index. Each index entry stores the employee ID (4\,bytes) and a pointer to the data block (3\,bytes). Index blocks are 512\,bytes. Determine (a) the minimum number of index blocks required and (b) the total storage (data blocks + index blocks) in kilobytes, rounded to the nearest whole kilobyte.

A. 36 index blocks; 1300 KB total storage

Correct B. 35 index blocks; 1268 KB total storage

C. 34 index blocks; 1240 KB total storage

D. 30 index blocks; 1200 KB total storage

Correct Answer: B

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Question 23 View Details

A small business invests \(\text{₦}500,000\) in a fixed‑deposit account that compounds interest annually. After 3\,years the amount has grown to \(\text{₦}632,000\). The business is considering an alternative monthly savings plan that pays a nominal annual interest rate of 5\% compounded monthly. What monthly deposit (to the nearest naira) must be made for 36\,months to obtain at least the same final amount of \(\text{₦}632,000\)?

Correct A. 16311

B. 17000

C. 15800

D. 15000

Correct Answer: A

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Question 24 View Details

In a data‑processing system the total time to handle a batch of transactions is 120\,seconds. The time is divided among the four stages—input, processing, storage and output—in the ratio 3\,:\,5\,:\,2\,:\,4. How many seconds are spent on the processing stage? Give your answer to two decimal places.

A. 60.00

B. 25.71

C. 34.29

Correct D. 42.86

Correct Answer: D

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Question 25 View Details

A data transmission uses 7‑bit ASCII characters with an added even‑parity bit, forming an 8‑bit byte. The character ‘I' (ASCII 73) is transmitted. Its correct 8‑bit code with even parity is therefore sent. During transmission a single‑bit error occurs and the receiver obtains the byte 01001001. Assuming at most one bit is wrong, identify the position (1 = leftmost) of the erroneous bit.

A. 8

B. 2

Correct C. 1

D. 4

Correct Answer: C

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