SST 2018 Prelim P1 Solution

1 2018 SEC 4 COMPUTING PRELIM PAPER 1 MARKING SCHEMES Qn 1 Marking Scheme / Answer Marks (i) A byte is a unit of data (or memory) that is made up of eight bits. 1 (ii) A gibibyte = 1024 mebibytes = (1024)2 kibibytes = (1024)3 bytes. = 230 bytes. Hence x = 30. 1 (iii) 256 000 000 000 bytes = 256 GB 4 TB = 4 000 000 000 000 bytes or 4×1012 bytes 1 1 Qn 2 Marking Scheme / Answer Marks (i) Dave is wrong. A 64-bit computer can theoretically access 264 bytes of memory, which is about 18 exibytes; a 32-bit one can access only 232 bytes, which is about 4 gibibytes. 2 (ii) (A) A modern computer is likely to have 8 gigabytes of RAM installed. 1 Qn 3 Marking Scheme / Answer Marks (a) (2E7)16 = (2 x 16^2) + (14 x 16) + (7 x 1) = 743 2 (b) (10 1011 1101 0000 0100)2 = (2BD04)16 2 (c) (3172)10 = (C64)16 2 Qn 4 Marking Scheme / Answer Marks (i) Possible quantities • Number of friends • Hourly rental fee for the karaoke room, in Singapore dollar • Service charge in percentage • Government tax in percentage 2 (ii) Input Output hours : number of hours spent, rounded up to smallest integer greater or equal to itself. FnB: Amount, in Singapore dollars (SGD), spent on food and beverages. N: Number of friends F: Hourly rental fee for the karaoke room, in Singapore dollar. Cost_per_pax : Amount of money, in Singapore dollars (SGD), to be paid by each friend. 3 (iii) Sample modified pseudo-code: INPUT hours, x, N, F Cost_per_pax = (F*hours + (x × 1.07 × 1.1) ) / N OUTPUT Cost_per_pax 2 Qn 5 Marking Scheme / Answer Marks (i) 3 (ii) 1 repeat 3 (step) 2 repeat 4 (left step left repeat 4(step left) right step) right 2 Qn 6 Marking Scheme / Answer Marks (i) 6 1 (ii) “I love it!” 3 (iii) 2 1 (iv) The output represents the number of words in the list words that has more than 2 vowels. 1

2 Qn 7 Marking Scheme / Answer Marks (a) N = 1 L i Output [7] 0 [7] 1 (b) N = 2 L i j Output [5, 3] 0 0 [3, 5] 1 1 [3, 5] 2 (c) N = 4 L i j Output [7, 1, 5, 3] 0 0 [1, 7, 5, 3] 1 [1, 5, 7, 3] 2 [1, 5, 3, 7] 3 1 0 1 [1, 3, 5, 7] 2 2 0 1 3 0 [1, 3, 5, 7] 3 (d) It sorts a given list of number in ascending order. 1 Qn 8 Marking Scheme / Answer Marks 1 highest = 0 Error 1: Line 4 Type: run-time error Correction: number = int(input("Enter a number:")) Error 2: Line 5 Type: syntax error Correction: if number > highest: Error 3: Line 6, 8 Type: Logic error Correction: highest = number, lowest = number 2 lowest = 0 3 for i in range(100): 4 number = input("Enter a number:") 5 if number > highest 6 number = highest 7 if number < lowest: 8 number = lowest 9 print(highest, lowest) 2 2 2

3 Qn 9 Marking Scheme / Answer Marks Code Snippet Types of Validation Check not year.isnumeric() Range Check len(year)!=4 Format Check len(year)==0 Presence Check if (year<0 or year>9999): Length Check 3 Qn 10 Marking Scheme / Answer Marks IPV4 Address / IPV6 Address / Mac Address (Accept just IP Address) 2 Qn 11 Marking Scheme / Answer Marks (1) Protocol (to use) (2) Domain Name of Web Server (3) Path of page to request 3 Qn 12 Marking Scheme / Answer Marks (a) Phishing refers to the use of emails to steal personal information from users. These details could then be used to commit a range of frauds such as buying goods or services using the details or even taking out loans by forging a person’s identity. 2 (b) Communicate personal information in person or through secured web sites only. Do not click on links, download files or open attachments in emails from unknown sources. Check online accounts and bank statements regularly to ensure that no unauthorized transactions have been made. 2 Qn 13 Marking Scheme / Answer Marks (a) The OR gate 1 (b) A B C D E F G X 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 1 0 0 1 1 1 1 0 1 1 0 1 0 0 0 1 0 0 0 0 1 0 0 1 0 1 0 1 0 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 0 0 1 3 (c) 5

4 Qn 14 Marking Scheme / Answer Marks (a)(i) Text 1 (a)(ii) Number 1 (a)(iii) = (-B$2 + sqrt(B$2*B$2-4*B$1*B$3))/(2*B$1) OR = (-$B$2 + sqrt($B$2*$B$2-4*$B$1*$B$3))/(2*$B$1) 2 (b) Ken received cash by taking a special loan package. He receives $3000 initially and for the next 24 months, receives $100 month. The bank charges 2% interest per month and at the end of the 24 months loan period, Ken has to return to the bank a lump sum amount of $7867.50. 3 Qn 15 Marking Scheme / Answer Marks • For client-server networks, centralised control of data and resources makes it easier to schedule backups of all shared files at regular intervals as compared to P2P networks where data and resources are stored locally within each computer. For example, Synology software and hardware backup network resources to a Network-attached Storage (NAS). • For client-server networks, security may be enhanced as access rights can be controlled centrally at a server as compared to P2P networks where security is handled by each computer. For example, antivirus software such as MacAfee can be installed. 2 • For client-server networks, there is a higher setup cost due to the need for a higher-performance server. For P2P networks, the setup cost is lower as basic computers can act as servers. • For client-server networks, there is administrative costs needed for the maintenance of server and clients which will not be incurred for P2P networks. 2 Qn 16 Marking Scheme / Answer Marks (a) Teleworking is working from home by using technology to support communication and work. 1 (b) Phone / Conference calls are cheaper using VoIP. 1 (c) (i) 1 mark for any of the following: o Less time is spent on commuting for meetings o Meetings can be organised and held at any time o People do not have to spend time away from their families (ii) 1 mark for any of the following: o Face to face contact is still considered important for meetings o People may not be able to focus so well on work if they work from home o May be difficult to arrange a meeting when people are in places of different time zones 2