SRSS 2020 P1 Solution

1 Serangoon Secondary Computing Sec 4E 2020 Preliminary Exams (Marking scheme) Q1a) [4 m] Logic gates Boolean Values A B X 0 0 1 0 1 1 A B X 0 0 0 1 1 1 A B X 0 1 0 1 1 0 A B X A B X A B X A B X

2 Q1b) [5m] X = (A OR (NOT B NAND C)) AND (A NOR B) Q1c) [4 m] A B C D (NOT B) E (D NAND C) F (A OR E) G (A NOR B) X (F AND G) 0 0 0 1 1 1 1 1 0 0 1 1 0 0 1 0 0 1 0 0 1 1 0 0 0 1 1 0 1 1 0 0 1 0 0 1 1 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 1 0 1 1 0 0 B A C X

3 Q2) [5 m] (a) The network interface card is the hardware interface that enables the transfer of data between a device and a network. (b) The network switch is a device that constructs a single network by connecting two similar networks together. (c) The modem is a device responsible for modulating and demodulating digital data when data is transmitted over long distances. (d) The router is a device that forwards packets between separate networks. (e) The network hub is a device that transmits received packets to all connected devices. Q3a) [4 m] Any 2 social benefits from: • Enabled communication between people without face-to-face meetings. • Enabled students to learn from home through the use of online learning tools and virtual classrooms tools. • Allowed people to entertain themselves while staying at home (e.g. mobile gaming communities, live video streaming etc) • Keep people updated with latest news. • Encourages community driven efforts that benefits the society during the lockdown (e.g. donation drives, food distribution drives etc) • Any other relevant answers. Any 2 economic benefits from: • Allowed business to reach out to customers through online marketing and social media when retail businesses were required to shutdown. • Reduced business costs from overseas travel with the use of cheap and effective video conferencing tools in place of face-to-face meetings. • Enabled consumers to spend, borrow, invest and save money through electronic applications without the need for face-to-face interactions. • Create job opportunities such as online food delivery and delivery. • Any other relevant answers. Q3b) [2 m] Any 2 negative impacts from: • People are easily misled by the spreading of rumours and false information online. • Cyberattacks and cybercrimes targeted at vulnerable groups of people lead to loss of money. • Increase in cyber addiction rates which may lead to deficiency in real-life social skills and abandoning of responsibilities. • Excessive screen time may lead to health problems (e.g. insomnia, eyestrain, increased anxiety etc). • Any other relevant answers

4 Q4a) [2 m] (1 0 0 1 0 1 1 0)2 = 21 + 22 + 24 + 27 = 2 + 4 + 16 + 128 = 150 Q4b) [2 m] Denary Quotient Remainder 459 28 11 (B) 28 1 12 (C) 1 0 1 459 = 1CB16 Q4c) [3 m] Any 3 relevant points from: • Represented by 3 bytes of data (6 hexadecimal digits); 1 byte of data to represent each of the intensities of red, blue and green colours. • Each colour intensity ranges from 00 (lowest intensity) to FF (highest intensity). Range of colours from 000000 to FFFFFF • If all three colour intensities are 0 (000000), the resulting colour is black. If all three colour intensities are F (FFFFFF), the resulting colour is white. • RGB colour code displayed in the form RRGGBB, where RR, GG and BB are two-hexadecimal numbers ranging from 0 to F. • 16,777,216 different colours can be represented using the RGB colour code. • RGB colour codes are used in websites using HTML or CSS. Q5a) [1 m] Number / integer Q5b) [2 m] = ($C$3 * B7) + ($C$4 * C7) OR = (C3 * B7) + (C4 * C7) Q5c) [2 m] Any 2 relevant points from:

5 • Cells C3 and C4 must be absolutely referenced for the formula in cell D7 (if answer in 5b shows absolute referencing, assume student has stated this point) • Select cell D7, (right-click) copy the cell and (right click) paste on cells D8 to D11 • Select cell D7, move mouse to the bottom right corner of the cell until a plus-shaped (+) cursor can be seen; click and drag the cursor all the way to cell D11 Q5d) [2 m] =IF(D7>E7,”Profit”,”Loss”) Q6) [5 m] 1 to 2 correct statements matched: 3 to 4 correct statements matched: 5 to 6 correct statements matched: 7 to 8 correct statements matched: All statements matched correctly:

6 Q7a) [2 m] Any 2 relevant input devices from: • Barcode scanner / Scanner / Camera • Number pad / Keyboard / Touchscreen panel • Thermal scanner Q7b) [4 m] Any 4 relevant modules from: • NRIC barcode scanning module • Contact number form module • Database search modules (accept any meaningful names, limit to 1 only) 5 7 2 1 4 6 3 8 9

7 • Databae sentry modules (accept any meaningful names, limit to 1 only) • Gantry operation module • LCD display module Q7ci) [2 m] Variable Data Type valid_contact boolean contact_num string Q7cii) [2 m] Both answers in any order: • Length check • Format check Q7ciii)[2 m] Test case condition Test data Normal Accept any telephone number that start with “6” or “9” and is exactly 8 characters long. E.g. 91234567 Error Accept any telephone number that does not start with “6” or “9”, or is not exactly 8 characters long. e.g. 12345678, 9876543 Q7civ) [2 m] Line number: 09 Changed line: IF contact_num[0]!="9" or contact_num[0]!="8" or contact_num[0]!="7" or contact_num[0]!="6" OR IF contact_num[0] NOT IN ["6","7","8", "9"] Q8a) [5 m]

8 Accept Reject Count Sack OUTPUT 0 0 0 49.2 7, 3 1 1 1 50.4 2 2 2 49.5 3 3 3 50.2 4 4 50.0 5 5 49.7 6 6 50.1 7 7 51.3 8 50.5 9 50.6 10 Q8b) [1 m] Any 2 relevant points from: • Input 10 floating point (decimal) numbers • Counts the number of accepted values (more than or equal to 49.5 and less than or equal to 50.5) and rejected values • Outputs the number of accepted and rejected values. Q8c) [2 m] Both changes in any order: • Change “Is Count = 10?” to “Is Count = 30?” • Remove “Is Sack < 49.5?” symbol.

9 Q9) [8 m] All 4 errors in any order: • Error 1: line 04 Correction: WHILE Number < 0 OR Number > 100 • Error 2: line 08 Correction: NumArray[Index] = Number • Error 3: line 09 Correction: IF Number >= 50 THEN Count = Count + 1 • Error 4: line 10 Correction: Until Count = 40 NEXT Index OR entire line 10 is removed Q10) [7 m] - Initialization of 2 variables to count number of days each city had a higher daily average temperature - Initialization of 2 variables to record the highest daily average temperature in City A (set to a very low value) and lowest daily average temperature in City B (set to a very high value. - Loop management 365 repetitions - Input 2 temperatures values - Compare the 2 values - …… and increase count for city with higher temperature - Check if value input for City A is higher than the highest recorded value for City A - …… and update as highest value if it is higher - Check if value input for City B is lower than the lowest recorded value for City B - …… and update as lowest value if it is lower - Output the 4 pieces of data Sample algorithm: CityACount = 0 CityBCount = 0 CityAHighest = -999 CityBLowest = 999

10 FOR Days = 1 to 365 Input CityA, CityB IF CityA > CityB CityACount = CityACount + 1 ELSE IF CityB > CityA CityBCount = CityBCount + 1 ENDIF IF CityA > CityAHighest CityAHighest = CityA ENDIF IF CityB < CityBLowest CityBLowest = CityB ENDIF NEXT Days OUTPUT 'City A had ' + CityACount + ' days with a higher daily average temperature.' OUTPUT 'City B had ' + CityBCount + ' days with a higher daily average temperature.' OUTPUT 'The highest daily average temperature recorded in City A was ' + CityAHighest OUTPUT 'The lowest daily average temperature recorded in City B was ' + CityBLowest