2018 SRSS P1 Answers

1 Serangoon Secondary Computing Sec 4E 2018 Preliminary Exams (Answers) Q1) Description Function Q2) a) = 18110 b) F16 = 1510 = 11112 816 = 810 = 10002 = 1111 1000 c) Denary Quotient Remainder 250 ÷ 16 15 1010 = A16 15 ÷ 16 0 1510 = F16 = FA16 128 64 32 16 8 4 2 1 1 0 1 1 0 1 0 1 Returns number rounded up to a given multiple MODE SMALL ROUND Returns the most repeated number in a set of numbers Use to retrieve the nth lowest number from a set of numbers CEILING

2 Q3) Cause of error Description (any one point) Prevention (any one point) Integrity of data (any one point) Authentication • process of verifying the identity of a user • password • security tokens • Two-factor authentication / OTP • biometrics • someone other than the user can have access to personal data and • perform unauthorised transactions without the user knowledge Access control • Permissions to control ability to view or make changes to the contents of folder or files • Set permissions to members only based on types of user / group of users • Privacy settings • Firewall • Encryption • Data not meant for certain users to view / modify can be compromised accidentally Privacy policy • Rules and practices that govern how the data can be accessed • Implement a Data Protection Act • Read and understand the privacy policy of the organisation providing the service • Unauthorised access can also occur indirectly due to the actions of third-party users or services.

3 Q4) Q5) A bus is used to transfer bits of data between the different components found on the motherboard One such component is the ROM which stores the instructions to the start-up the computer. Q6) a) Device: - Network Interface Card (NIC) Function: - Provides the hardware interface to .. - enable the transfer of data between a device and a network b) Device: - Bridge / Switch Function - Device that constructs a single network by connecting two similar networks together - Has more intelligence, send packets only to intended recipients thus avoiding less data congestion (data travelling at any point in the network c) Device: - Router / Getway Function: - Device that forwards paclets between separate networks - Chose the best route to transfer to destination network - Uses IP address to transfer data Statement Interpreter Compiler takes one statement at a time and executes it ü generate an error report at the end of translation of the whole program ü stops the translation process as soon as the first error is encountered ü slow speed of execution of program loops ü translates the entire program in one go ü

4 Q7) a) Any three from • IP address – Used by Internet Protocol to o identify the network and host address of the devices o Logical address (may change / not fixed) o IPv4 address take the form of a 4 bytes or group (IPv4 32-bits) • MAC address – Media Access Control to o Identify the computer in the local network o Physical address (fixed / unique for every device) o Made up of 6 bytes or group (48-bits) b) Parity bit is used for error detection in data transfer c) Any two from • The receiver detects an error in the data packet because • for odd parity there should odd number 1 bits • instead there are even number (four) of 1 bits at the receiver d) Any one from • Parity bit can only detect single bit or odd number of bit errors. • It does not know which bit has been corrupted, so • It cannot do error correction

5 Q8) Inputs : • List of shops with • corresponding phone model price and discount rate Outputs: • Shop name with • the price of the phone model that cost the least Processes required: • Store the data in the array / list • Initialize the lowest price variable • Compute the price after applying discount for each shop • Compare the price with the lowest price • Update lowest price if it is lower Q9) a) Any one from: • Error 1 : Line 1 • Correction : Small = 999 • Error 2 : Line 5 • Correction 2 : IF Num < Small THEN Small = Num • Error 3 : Line 8 • Correction 3 : UNTIL Counter = 30 or UNTIL Counter > = 30 or UNTIL Counter > 9 • Error 4 : Line 7 • Correction 4 : PRINT Small should come after the end of the repeat loop • or line 8 should come before line 7 b) i. Any two from: • the input Num has to be stored in an array or list because • all the input numbers is needed • for later use in the program ii. NumberList = NumberList + [Num] or any similar notation

6 Q10) a) b) A T S Working Space Y 0 0 0 0 0 0 1 0 0 1 0 1 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0

7 Q11) Engine Count Number Size Average Output 0 0 0 1.8 1.8 1 1 2.0 3.8 2 2 1.0 4.8 3 1.3 6.1 4 1.0 7.1 5 2.5 9.6 3 6 2.0 11.6 4 7 1.3 12.9 8 1.8 14.7 5 9 1.3 16.0 10 -1 1.6 1.6, 5

8 Q12) Marking points • correct loop • correct inputs • check for type and calculate itemcost • action taken if type NOT 1, 2 or 3 • calculate totalcost • calculate the average totalcost • both outputs in the correct place Sample algorithm: total cost = 0 for x = 1 to 1000 input type, partcost ( if type = 1 then itemcost = partcost * 1.5 if type = 2 then itemcost = partcost * 2.5 if type = 3 then itemcost = partcost * 5.0 else print error totalcost = totalcost + itemcost print itemcost @ next x average = totalcost/1000 print average @