SRSS Sec 4 COMP PRELIM 2022 PAPER 1 MS

Serangoon Secondary Computing Sec 4E 2022 Preliminary Exams (Marking scheme) 1. (a) Cell Data type A1 String / Text [1m] A3 Date [1m] C6 Currency [1m] D4 String / Text [1m] (b) SUM [1m] (c) = SUMIF(D2:D6 , “credit card” , C2:C6) use of =SUMIF [1m] correct range for evaluation and criteria [1m] correct range for summation [1m] 2. (a) A cyberattack is an unwelcomed attempt to steal, expose, alter, disable or destroy information through unauthorised access to computer systems. It is usually carried out over a network such as the ……………………………………… . One type of cyberattack is ……………………………………… This is a type of malware that downloads onto a computer disguised as a ……………………………………… program and attacks a computer by enabling intruders to open backdoors for unauthorised access to the computer. A second type of cyberattack is ……………………………………… . This is a form of social engineering attack which sends fraudulent communications that appear to come from ……………………………………… sources in order to steal personal information such as passwords and credit cards numbers from users. Internet [1m] Trojan-horse [1m] harmless [1m] phishing [1m] reputable [1m]

(b) Problem Effect Preventive measure Power failure Any one of: • Data corruption if data is in the midst of being save • Data lost if data has not been saved [1m] Any one of: • Set up of backup power supply or UPS (Uninterrupted Power Supply) • Make regular backups of data [1m] Human error Any one of: • Accidental deletion or over- writing of data. • Accidental damage to storage medium (e.g. transport or spillage of water) [1m] Any one of: • Set up of file sharing rules and rights • Adequate protection to storage medium (e.g. avoid eating/drinking near devices, and protection during transport • Make regular backups of data. [1m] Hardware failure Any one of: • Data corruption due to hardware failure of storage device • Data loss due to hardware failure of storage device [1m] Any one of: • Check storage devices regularly and replace them when signs of failure are detected • Use of redundancy storage solutions such as RAID systems • Make regular backups of data [1m]

3. Function Description [1m] for each correct line COUNT COUNTA COUNTIF LARGE MAX Counts the number of cells in a range that contain numbers, currencies, dates, times and percentages Counts the number of cells in a range that are not empty Counts the number of cells in a range that meet a given condition Finds a numeric value based on its position in a list when sorted by value in descending order Finds the largest numeric value in a given range of cells Rounds a number up to the nearest level of significance

4. (a) (i) Feature that is the same [1m] Any one from: • Connects 2 or more devices together to allow them to communicate with each other. • Has ports to connect LAN cables Difference [1m] Any one from: • Switches connect multiple similar networks together, but routers allow separate networks with different protocols to communicate with each other. • Switches forward data packets to a device’s MAC address, but routers forward data packets to a device’s IP address. (b) Belinda’s home network is a …………………………………… Reasons ([1m] for each correct point): • Devices connected within a small area • Small number of devices connected on the network 5. (a) Truth table Correct or incorrect Correct solution (where needed) A B A AND B 0 0 0 0 1 1 1 0 1 1 1 1 incorrect A B A AND B 0 0 0 0 1 0 1 0 0 1 1 1 [1m] A B A NAND B 0 0 1 0 1 1 1 0 1 1 1 0 correct A B A NAND B 0 0 0 1 1 0 1 1 [1m] A B A NOR B 0 0 0 0 1 0 1 0 0 1 1 1 incorrect A B A NOR B 0 0 1 0 1 0 1 0 0 1 1 0 [1m] LAN [1m]

(b) X = (A NOR B) NAND (B OR NOT C) A B X C Note: marks will be awarded only if correct gate and correct inputs/output are drawn (c) A B C Working space X (D NAND F) D (A NOR B) E (NOT C) F (B OR E) 0 0 0 1 1 1 0 0 0 1 1 0 0 1 0 1 0 0 1 1 1 0 1 1 0 0 1 1 1 0 0 0 1 1 1 1 0 1 0 0 0 1 1 1 0 0 1 1 1 1 1 1 0 0 1 1 [1m] [1m] [1m] [1m] [1m] [1m] [1m] [1m]

6. (a) Stage Letter 1 to 2 correct: [1m] 3 correct: [2m] 4 correct: [3m] 1 A 2 C 3 D 4 E 5 B (b) Any 2 from: [1m] each • Technique of breaking down a complex problem or process into smaller parts called sub-problems • Each sub-problem is more manageable and easier to understand • Sub-problems can be solved individually and combined to solve the original problem • Incremental and modular approaches (c) Any one from: [1m] • Sensing a swipe action of the touchscreen panel from a start point to an end point • Determine the direction of swipe by the user on the touchscreen panel • Generating graphics to show a change of direction of movement of the game character (d) Freeware Any 2 from: [1m] each • Proprietary software • Available for use at no cost • Illegal to copy and modify source codes • Legal to copy and distribute freeware Open-source software Any 2 from: [1m] each • Freedom of use of the software. Users may still need to pay to use open-source software • Users are free to change, copy, study and share software and its source codes • Conditional for users to maintain open-source licensing, and attribution given to original authors for any derivatives from the original source. (e) Open courseware [1m]

7. (a) All 4 in any order from: • Error: Line 4 [1m] Correction: WHILE Num != 0 [1m] • Error: Line 10 [1m] Correction: Flag[Count] = TRUE [1m] • Error: Line 17 [1m] Correction: IF Flag[Count] == TRUE THEN [1m] • Error: Line 18 [1m] Correction: OUTPUT Large[Count] [1m] (b) All 2 in any order from: • Error type: Syntax error [1m] Description: Errors due to incorrect source code, such as spelling mistakes or wrong use of symbols, that fail to follow rules of the language. [1m] • Error type: Run-time error [1m] Description: Errors that are only detected while a program is running; usually caused by erroneous data or the wrong use of commands which causes the program to crash or hang. [1m] (c) Test case condition Test data Normal 5 (or any other integer number) [1m] 0 [1m] Error TRUE [1m] “Five” [1m] Or any other acceptable answer (d) Debugging technique: Use of intermittent print statements [1m] Description: Any one from: [1m] • Adding print statements to display values of variables • Adding print statements in a loop to observe change of variable values as a loop repeats

8. One mark for each (max of 7 marks): • Input a number and initialize to a variable (number to be guessed) • Management of while loop • …… that repeats until a correct answer is given • Input player’s guess in every loop • Checks if player’s guess is larger than answer • …… and outputs an appropriate message when guess is larger than answer • Checks if player’s guess is smaller than answer • …… and outputs an appropriate message when guess is smaller than answer • Outputs “You win!” when the correct answer is given by the player • Outputs the number of guesses Possible algorithm: OUTPUT “Please enter a number for player to guess: ” INPUT ANS WHILE TRUE: OUTPUT “Guess the number: ” INPUT GUESS IF GUESS < ANS THEN OUTPUT “Number too small. Guess a larger number.” ELSE IF GUESS > ANS THEN OUTPUT “Number too larger. Guess a smaller number.” ELSE: OUTPUT “You win!” BREAK END WHILE