TSS 2019 P1 Solution

2019 Prelim 4E Comp P1 Marking Scheme Question Answer Marks 1 Number Currency Text Date COUNTA √ RAND √ SMALL √ √ √ LEN √ 1 mark for each row 4 Question Answer Marks 2(a) Headings OR Header OR Field Name Text Not accepted: Title 2 2(b) ROUND() 1 2(c)(i) =VAR(E3:E18) 1 2(c)(ii) STDEV() 1 2(d) MODE.SNGL() 1 Question Answer Marks 3 PMT() calculates the instalment for a loan with compound interest. PPMT() calculates the portion of the instalment that is used to reduce the principal of the loan. Not accepted: monthly payment / principal payment 2 Question Answer Marks 4 Sum of place-values method, and Division-by-2 method 2 Question Answer Marks 5 Hexadecimal/ Binary Each character in the ASCII code is represented by a 2-digit hexadecimal or 7-bit binary 2 Question Answer Marks 6(a) Any 2 relevant points: Hackers may encrypt critical data and ask for ransom. OR Leaked or altered confidential data may compromise the proper operation of the university, e.g. exam papers and exam results. OR Personal and private data may be exposed, resulting in identity theft. E.g. NRIC numbers OR Intellectual property may be stolen or lost. Not accepted: Data is stolen (too vague) 2

6(b) Any 2 relevant points: Allow only authorized storage devices to be connected to the computer network. OR Use an email filter to block suspicious email and email attachments. OR Encrypt all important data so that hackers will not be able to read the data. OR Use encryption in data communication with between computers on the network. OR Isolate the Local Area Network from the Wide Area Network to prevent access from external computers. 2 Question Answer Marks 7(a) Phishing uses emails and fake websites that appear to be from reputable companies in order to steal personal information. Pharming intercepts requests sent from a computer to a legitimate website and redirects to a fake website to steal personal data. 2 7(b) A virus attaches itself to a harmless program and modifies it so that when it is run, the virus attaches copies of itself to other programs. A worm is a computer program that runs automatically and sends copies of itself to other computers. 1 mark if only mentioned about whether it attaches itself to a program 2 Question Answer Marks 8(a) Read the privacy policy of the organization. 1 8(b)(i) It may lead to identity theft if he does not use encryption when uploading the photo of the NRIC. OR It may lead to identity theft if he encounters a phishing website. OR It may lead to identity theft if his phone has a cloud service that backs up the NRIC photo to online servers without proper access control. Note: identity theft must be mentioned. 1 8(b)(ii) Ensure that the website uses public key encryption (padlock icon) or its address starts with “https:” OR Call the company first to verify that the website address is legitimate. OR Turn off cloud service and delete the photo immediately after uploading. 1

Question Answer Marks 9(a) The central processing unit is the part of the computer that processes data and follows instructions. 1 9(b) The computer bus is a collection of wires for transporting data from one part of the computer to another. 1 Question Answer Marks 10(a) A memory where stored data is lost when power supply is interrupted. 1 10(b) Data stored on a RAM can be easily changed while data stored in a ROM cannot be easily changed. 1 Question Answer Marks 11 Z= (A’ AND B) OR [(B AND C) AND (B’ OR C)] 1m – A’ AND B, B AND C 1m – B’ OR C 1m – [… and …] 1m – Z = … OR … 4 Question Answer Marks 12 One mark for each for correct gates used at each level of immediate output. 4 Question Answer Marks 13(a) Device responsible for modulation and demodulation. 1 13(b) A hardware interface/module that enables the transfer of data between a device/computer and a network. 1 Question Answer Marks 14(a) Wired networks have higher bandwidth than wireless networks Wired networks have dedicated connection while wireless networks are prone to interference from other devices that produce radio waves or microwaves OR susceptible to signal loss over a certain distance. OR bandwidth decreases greatly with more connected wireless devices 2

14(b) Wireless networks have better scalability than wired networks Adding more devices on a wired networks requires additional cables and network devices since ports are limited. Adding more devices on a wireless network just require some network settings. 2 Question Answer Marks 15 In client-server networks, data and resources are shared using one or more dedicated servers, while in P2P networks, these are shared directly between computers. In client-server networks, each computer has a distinct role: client or server, while in P2P networks, each computer acts as both a client and server. 2 Question Answer Marks 16 3 Question Answer Marks 17(a) 0 1 1 1 1 0 1 1 1 17(b) The other method is using a checksum. 1 Question Answer Marks 18(a) Input(s) Output(s) Username: a string of characters that matches a username in the database of the website. Password: a string of characters that matches the password of the corresponding username in the database. Status: a string of characters that informs the user whether login is successful or not. Accepted:- Button: whether login button is clicked or not 3

18(b) Firstly, the program searches for the username in the database. If username is found, check whether password input matches the saved password of the username in the database If username is found and password matches, output “Login is successful!” Otherwise output “Login failed!” 3 Question Answer Marks 19(a) It is the breaking down of a complex problem or process into smaller and more manageable parts. Accepted: difficult problem into easier/simpler sub-problems Not accepted: program instead of problem 1 19(b) Any two logical sub-problems:  Find the largest common factor between two integers o Find all factors of an integer o Compare and identify the largest common factor between two integers  Divide an integer by a factor/divisor to find a quotient 2 Question Answer Marks 20(a) count a b OUTPUT 0 7 2 Win 1 4 4 Draw 2 8 9 Lose 3 One mark for each column. 4

20(b) 1m – Correct blocks for Start/End, Input a,b 1m – Initialize count, increase count by 1 1m – Decision block for case-otherwise (accept 2 decision blocks if sequence is correct: >b, =b) 1m – Three correct outputs with inverted commas 1m – Decision block for repeat-until -1 mark if any arrows missing -1 mark if wrong block shape -1 mark if flowchart lines are missing, incomplete or wrongly connected 5 Question Answer Marks 21 Order Stages of Program Development 1 Gather requirements 5 Implement code 2 Plan solutions 4 Test and refine code 3 Write code One mark deducted for a single mistake, e.g. 2↔4, otherwise no marks. 2

Question Answer Marks 22 Programming Construct Python Code Sequence count=0 total=0 Selection if x>0: count+=1 else: count-=1 Iteration for x in range(3): print(x) (any 2 rows) 1m awarded if both construct names are correct 1m awarded if one construct name is correct with correct python code 2m awarded if both construct names are correct and one correct python code 3 Question Answer Marks 23(a) A run-time error is an error that occurs while a program is running. 1 23(b)(i) Syntax errors may occur due to spelling mistakes OR due to incorrect sequence of symbols in source code 1 23(b)(ii) Logic errors may occur due to incorrect or incomplete algorithm. OR when the program does not give the expected output. 1 Question Answer Marks 24(a) A translator t