SPS 2019 P1 Solution

READ THESE INSTRUCTIONS FIRST Write your name, class, index number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Approved calculators are allowed. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. You should show all your working. The total number of marks for this paper is 80. Parent’s Signature : ____________________________ Date: ____________________________ Remarks (if any) : For Examiner’s Use Marks /80 Total % This document consists of 11 printed pages including this page. ST. PATRICK'S SCHOOL PRELIMINARY EXAMINATIONS 2019 SECONDARY 4 EXPRESS NAME SOLUTIONS CLASS INDEX NUMBER COMPUTING Paper 1 Written 7155/01 10 May 2019 2 h Candidates answer on the Question Paper. No Additional Materials are required.

2 1 Draw a line to match the spreadsheet function to the correct description. Function Description ROUND Looks in the first column of an array and moves across the row to return the value of a cell COUNTA COUNT Returns the periodic payment for an annuity VLOOKUP Rounds a number to a specified number of digits HLOOKUP Counts how many values are in the list of arguments PMT [4] 2 A security system records video footage. One minute of video requires 180 MB of storage. The recording system can store several hours of video footage. (Computer Science P1, CIE 2015) (a) Name and describe a suitable storage device for this recording system. Memory card / Solid state drive / Hard disk drive. It is a non-volatile secondary storage device *that is portable and uses flash memory / that uses flash memory / that uses magnetic storage. [2] (b) Calculate how much storage would be needed for 2 hours of video footage. Show your working and give the answer in Gigabytes (GB). 180 * 109 * 2 * 60 / 1012 = 21.6 GB [2]

3 3 A car’s Engine Management System receives information from seven different sensors and stores the status of each sensor in an 8-bit register. A value of 1 indicates a fault condition. For example, a register showing 10110100 indicates: • Engine overheating • Airbag malfunction • Low fuel (a) Identify the fault condition(s) that the following register indicates: 1 0 0 0 1 1 0 1 There is low fuel, low voltage and the brake pads are too thin. [2] (b) The system uses even parity. Write the correct parity bit in each of the following registers. 0 1 1 1 0 0 1 0 1 0 1 0 1 0 1 0 [2] (c) State the hexadecimal value of the binary number shown in (a). (8C)16 [1] Parity Bit CO level too high Low voltage Airbag malfunction Engine overheat Low fuel Low oil level Brake pads too thin

4 4 In 2018, many Apple users received the following email notification allegedly from Apple’s billing department. The hyperlink, titled “Click For Cancel or Downgrade >”, leads to a fake website which looked like the company’s real website. Several unsuspecting customers did not pay attention to the address of the hyperlink, and tried to login to their iTunes account as usual. As a result, their account was compromised, and personal information was stolen. (a) Name and explain the type of cyberattack involved. Phishing It uses emails and fake websites that appear to be from reputable companies in order to steal personal information from users. [3]

5 (b) Other than the address of the hyperlink, identify two tell-tale signs that should have alerted the user to conclude that the email is fraudulent, thus avoid becoming victims to this cyberattack. Any two of the following: • Email uses a generic greeting, “Dear Client”, suggesting that it was sent automatically and not by a person • Email has grammatical, spelling, spacing and punctuation errors, “Also,You can …”, “Click For Cancel or Downgrade”, that suggest it is not from a legitimate source • Tone of email is excessively urgent or threatening, “You will be billed each month unless you cancel.” It also continuously emphasises and hints to the recipient to cancel, downgrade, ask for full refund or ask for partial refund of the purchase, baiting the recipient to click on the hyperlink. • Email did not sign off, leaving no indication of the department or name of officer-in-charge. • The sender email address is questionable as it contains a long unintelligible string of characters and a dubious domain name, “contoloyo.com”, whereas most reputable companies tend to use more relevant user ID and domain names in their email addresses. • The recipient field displays “undisclosed-recipients:;”, indicating that the email was sent in mass to many others, instead of it being a receipt that is generated specific to the dedicated user. • The title of the email “Re: [Alerts – Recent Activtiy] Your payment has been Scheduled [CONFIRMATION]” shows that it is a reply email rather than an automated or newly sent receipt of purchase. [2]

6 6 A perfect number is an integer that is equal to the sum of its proper divisors. The following program will accept a sequence of integers and output the perfect numbers. 1 2 3 4 5 6 7 8 9 10 11 12 FOR counter = 1 to 3 total = 1 INPUT number FOR divisor = 2 to INT(number**0.5): IF number % divisor == 0: total = total + divisor + (number / divisor) ENDIF NEXT IF total == number: OUTPUT number ENDIF NEXT Complete the trace table for the following set of data, entered in sequence. number = 6, 10, 28, 30 Trace table counter total number divisor OUTPUT 1 1 6 2 6 6 2 1 10 2 8 3 3 1 28 2 17 3 4 28 5 28 [5]

7 7 In most cars, the car alarm system, A, would sound when • the user presses the alarm on the remote control (R = 1), or • the car is locked (L = 1) and the shock sensors detect a strong impact (S = 1), or • the car is locked (L = 1) and the voltage sensors detect a decrease in voltage (V = 0). (a) Write down the Boolean statement for the car alarm system. A = R OR (L AND S) OR (L AND NOT V) / A = R OR (L AND (S OR NOT V)) [1] (b) Draw the logic circuit diagram for the car alarm system. [4] 8 The following logic circuit diagram is only made up of NAND gates. (a) Complete the following truth table for the above logic circuit diagram. A B Q 0 0 0 0 1 1 1 0 1 1 1 1 [4] A R L S V A B Q

8 (b) Name a single logic gate that has the same function as the above logic circuit. OR gate [1] 9 The following program calculates the lowest common multiple between 2 integers. One way of calculating the lowest common multiple between 2 integers is to divide the product of the 2 integers by their highest common factor. 1 2 3 4 5 6 7 8 9 10 hcf = 0 Lcm = None INPUT integer_1, integer_2 FOR count = 2 to MIN(integer_1, integer_2) IF (integer_1 % count) == 0 or (integer_2 % count) == 0: hcf = count ENDIF NEXT Lcm = integer_1 * integer_2 % hcf OUTPUT Lcm (a) There are three errors in this code. Locate the errors and suggest a correction. Error 1 Line 1 Correction hcf = 1 Error 2 Line 5 Correction IF (integer_1 % count) == 0 and (integer_2 % count) == 0: Error 3 Line 9 Correction Lcm = integer_1 * integer_2 / hcf [6] 9 A processor or central processing unit (CPU) executes instructions. (a) Describe what is meant by a 1 MHz (megahertz) processor. a 1