SQSS 2018 P1 Solution

1 Computing 2018 Prelim P1 Mark Scheme Question Answer Marks 1 Description Function Returns the number of non-empty cells in the given range references ● ● COUNT ● HLOOKUP Looks for data in row and use associated data in the same row ● ● COUNTA ● CEILING Returns number rounded up to an exact multiple of significance ● ● VLOOKUP ● FLOOR 3 Question Answer Marks 2 One mark for the correct answer and one mark for showing the relevant working 2a (2^0) + (2^3) + (2^4) + (2^7) = 1 + 8 + 16 + 128 (Working) = 153 (Answer) 2 2b C 1100 7 0111 (Working) 1100 0111 (Answer) 2 2c 189 / 16 is 11 remainder 13 (working) BD (Answer) 2 Question Answer Marks 3a Pharming is the interception of request sent from a computer to a legitimate website and redirection to a fake website to steal personal data or credit card details. 2 Phishing is the use of emails and fake websites that appear to be from reputable companies in order to steal personal information such as passwords and credit card details. 2

2 Question Answer Marks 3b Two factor authentication is the type of authentication that uses evidence from both something the user knows and something the user owns. 1 Select either of the following: - Possibility of interception when sent wirelessly to user’s mobile phone during transmission process - Secret algorithm is poorly chosen or accidentally revealed, may be able to find out how to generate OTP without the use of the token 1 Question Answer Marks 4a modem 1 4b NIC 1 4c router 1 4d network bridge 1 4e network hub 1 4f SSID 1 Question Answer Marks 5a To perform basic mathematical and logical operations. 1 5b § Data bus is used to transport data between memory and the processor. § Address bus is used to specify memory address information. Difference is that data bus transport data in bi-directional while address bus is uni-directional. 3

3 Question Answer Marks 6a RAM – Random Access Memory is the main memory where data and instructions are stored temporarily. ROM – Read Only Memory is where data and instructions that rarely need to be change or used for starting up. RAM is volatile whereas ROM is not. 3 6b (1/2 Mark for each point mention) Device 1 – External hard disc drive Method – Data stored on Magnetic material Advantage – Large storage capacity, relatively cheaper Disadvantage – Vulnerable to drops and mechanical shocks 2 Device 2 – Flash drives, Memory Cards Method – Data is stored in electronics circuits that have no moving parts Advantage – much faster, portable, not as vulnerable Disadvantage – Much more expensive 2 Alternative Device – CD ROM, DVD, Blu-ray Method – Data is stored as very small pits or indentations that can be read or written by a laser Advantage – Large storage capacity of up to gigabytes of data Disadvantage - Data can only be written once for some non-rewritable formats - lower maximum storage capacity than magnetic external storage - Vulnerable to scratches and fingerprints

4 Question Answer Marks 7 One mark for each correct point Inputs - 150 student names - 150 student weights - 150 student BMI Outputs - Names of students who are obese - Weights of those students who are obese Processes required - Store the data in array / lists - Search for the students whose weight is above the obese weight / Compare students weight with the obese benchmark 6 Question Answer Marks 8 - Identifier, is a sequence of characters that follows certain rules and can be used as a variable name - List, is the data type for storing multiple values in a sequence - Type casting, is the process of converting a value from one data type to another 3 Question Answer Marks 9 8 Error : total = 1000 Correction : total = 0 Error : number + total = total Correction : total = total+number Error : IF total < 1000 Correction : IF total > 1000 Error : counter = counter -1 Correction : counter = counter +1

5 Question Answer Marks 10 5 X Pass Fail Check OUTPUT 0 0 42 1 -8 77 1 27 85 2 35 -5 30 2 -20 91 3 41 -15 0 3 ,2 Question Answer Marks 11a 5 X = (T AND (NOT L)) OR (A AND (NOT T)) T L A X

6 Question Answer Marks 11b 4 A T L X 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 Question Answer Marks 12 - Checksum is another method for checking - Calculated before transmission - If value is less than or equal 255, checksum remains the same - Else value is modulus of 256 - This value is sent together with the data and recalculated and compare at the receiving end to check if it matches. 4 Question Answer Marks 13(a) - Metropolitan Area Network (MAN) 1 13(b) - Local Area Network (LAN) 1

7 Question Answer Marks 14a - Radio Waves 1 One mark for advantage and one mark for disadvantage Advantage (any of the following) - Free from clutter - Scalability, easier to add new devices to the network Disadvantage (any of the following) - Less reliable due to potential interference from radio waves and microwaves - Generally slower and lower bandwidth - Higher cost - Less secure 2 Question Answer Marks 15 - Initialisation of counter and output list - Loop management ten repetitions - Input word - Exit to print out list of words if “Quit” is entered - Checking for word in output list - Appending the word to the output list if word not in list - Printing out the list of non-repeated words in order 8

8 Sample flowchart START Count = 0 Output_list =[ ] Is count <10? INPUT word Is word “Quit”? Is word in output_list? Append word to output_list Add 1 to count PRINT output_list Y N N Y Y N

9 Sample Algorithm using REPEAT …. UNTIL count = 0 Output_list = [ ] REPEAT INPUT word IF word = “Quit” ENDIF IF word not in Output_list Output_list = Output_list + word count = count + 1 ELSE count = count + 1 UNTIL count = 10 OR word = ‘Quit’ OUTPUT Count_list -------------------------------------------------------------------------------------------------------------------------------------- Sample Algorithm using WHILE…ENDWHILE count = 0 Output_list = [ ] INPUT word WHILE count <10 OR word is not equal to “Quit” IF word not in Output_list Output_list = Output_list + word count = count + 1 Else count = count + 1 INPUT word ENDWHILE OUTPUT Output_list

10 Reference MS Initialization of array or list for output User prompt to enter a word Loop management (exits loop when the word input by the user is “Q” Within the loop, check whether the word input is found in the output array/list …….if yes, ignore …….else, append the word input to the output array/list User prompt to enter the next word. End of loop Loop management to print out each item in the output array/list