SRSS 2019 P1 Solution

1 \Serangoon Secondary Computing Sec 4E 2019 Preliminary Exams (Marking scheme) Q1) [5] Network Term Description Q2) IP Address MAC Address Service Set Identifier Ring Topology Star Topology An identifier that is automatically assigned by a router. It is required to receive and forward data packets out of a network A network configuration that requires a central device such as a hub or a bridge to manage the transmission of data. A 32-byte long string that identifies a wireless access point and all devices connected to it. A network configuration where the entire network may fail whenever any computer in the network fails. An identifier that is required to receive and forward data packets within a network through a network bridge. A network configuration where all computers are connected together through a single common cable.

2 a) (10000101)2 = (1*128) + (1*4) + (1*1) = 133 or (133)10 [2] b) F16 = (1111)2 B16 = (1011)2 (FB)16 = 11111011 or (11111011)2 [2] c) (11110)2 = (0001 1110)2 = ( 1 E )16 = 1E or (1E)16 [2] d) (365)16 = (3 x 162) + (6 x 161) + (5 x 160) = 869 [2] Q3) (a) (i) [5] Highest Num1 Num2 Range i 1 15 6 15 1 1 6 2 3 3 4 5 6 (ii) [1] • Find the highest common factor of 2 inputs • Find the largest common factor of 2 inputs • Find the greatest common factor of 2 inputs (b) (i)

3 [2] Validation check: Presence check Description: To check that the user has entered a value in the inputs Validation check: Format check Description: To check that the user has entered only numbers in the inputs Validation check: Length check Description: To check that the user has entered at least 1 character/digit in the inputs Validation check: Range check Description: To check that the user has entered numbers greater than zero (ii) [2] • Presence check • Length check • Format check • Range check (c) [4] Test Case Condition Test Data Boundary condition 1, 1 Error condition 0, 10 Q4) (a) [2] • Poor authentication • Poor access control or authorization • Poor understanding of privacy policies (b) [2] • Use of passwords

4 • Use of security tokens • Use of Biometrics • Setting file permissions • Use of firewalls • Encryption of files (password protecting of files) • Reading and fully understanding privacy policies on use of services online • Use of anti-virus software (c) [4] • Cookies. Personal information stored in cookies can be stolen and misused. • Pharming. Interception of requests sent from a computer to a legitimate website and redirecting the user to a fake website to steal personal information. • Phishing. Sending of emails/text messages from fake websites that appear to be from legitimate reputable companies (e.g. banks). Users who are unaware will submit personal information to the phishing websites. • Spamming. Mass distribution of unsolicited digital content to email addresses or phone numbers collected from various sources. • Spyware. Having a hidden program that secretly collects personal information from its host computer and transmitting them to attackers without the host computer’s knowledge. • Trojan horse. A computer program that disguises itself to be a harmless program in a host computer but instead opens backdoors on the host computer to allow unauthorized access to attackers. • Virus. A malicious program that attaches itself to a normally harmless file and modifies (corrupts) it and subsequently attaches copies of itself to other programs. • Worm. A computer program that runs automatically and attempts to spread by sending copies of itself to other computers. It often affects computers by taking up bandwidth and memory which slows the computer down.

5 Q5) (a) [4] Household Device Input Component Output Component Washing Machine One from: • Selection knobs • Buttons One from: • Motor • LCD panel • Buzzer/Beeper Smart Mobile Phone One from: • Buttons • Touchscreen panel • Microphone • Camera • Fingerprint scanner One from: • LED display • Speakers • Headphones • Flash light (b) [3] Component: Central Processing Unit or Processor Functions: Any 2 from: • Arithmetic calculations • Perform logical functions • Controls flow of data in the computer • Decides when data is stored, received or transmitted in the computer (c) [3] • Storage device: Thumbdrive or other memory cards

6 Storage medium: Solid state Advantage: One from: § Faster read/write speed § Light weight and portable § Silent operation § Low power consumption • Storage device: CD/DVD or other optical medium Storage medium: Optical Advantage: One from: § Light and portable § Cheaper than SSD devices • Storage device: Hard disk drive (can be portable) Storage medium: Magnetic Advantage: One from: § Extremely large capacity § Relatively cheap considering storage capacity

7 Q6) (a) [4] (b) [4] F T P X

8 F T P Working Space X T AND F NOT P NOT P AND F 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 0 0 0 1 0 0 0 1 1 1 1 0 1 0 0 0 0 1 1 0 1 1 1 1 1 1 1 1 0 0 1 7) a) [8] • Error 1: Line 5 Correction: WHILE Guess != Answer • Error 2: Line 10 Correction: BREAK • Error 3: Line 13 Correction: Record[Count] = Guess • Error 4: Line 15 Correction: Count = Count + 1 (Single indentation. This statement must be within the While loop.) 8) a) [3]

9 A5 – Text / General D5 – Currency / Accounting / Money H10 – Date b) = C5 * $B$2 c) [2] = MAX(D5:D22) 9) (a) (i) [2] • Byte 5 • Byte 7 (b) (i) [1] • Byte 3 (ii) [1] • Column 7 (iii) [1] 1 0 1 0 0 0 0 0 (iv) [1] • Auto rectification of errors • Sender does not need to send data again when error is detected • Precise error can be located 10) [6] - Initialization of 2 variables to store highest score and count inputs - Loop management 32 repetitions

10 - Input name and score - …… and check if name is “DONE” then break - Input name and/or score in separate arrays - Check if score input is higher than the highest recorded score - …… and update as highest score if it is higher - Loop management to read scores from array - …… and output name and score of top student(s) Sample algorithm: Highest = -1 Count = 0 FOR i = 1 to 32 OUTPUT "Enter student name: " INPUT Name IF Name == "DONE" THEN BREAK ENDIF OUTPUT "Enter student score: " INPUT Score IF Score > Highest THEN Highest = Score ENDIF Namelist[Count] = Name Scorelist[Count] = Score NEXT i FOR j = 1 to Count IF Scorelist[j] == Highest THEN OUTPUT Namelist[j],Highest NEXT j