2021 ACSBR Computing P1 with Solutions

This paper has 14 pages, inclusive of the cover page. Name: Class: Index Number: Anglo-Chinese School (Barker Road) PRELIMINARY EXAMINATION 2021 SECONDARY FOUR EXPRESS COMPUTING PAPER 1 7155/01 2 HOURS INSTRUCTIONS TO CANDIDATES: Do not open this booklet until you are told to do so. Write your name and index number clearly in the spaces at the top of this page. Write in dark blue or black pen. You may use soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, 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 of question. You should show all your working. The total mark for this paper is 80. TOTAL 80

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 2 Secondary 4 Express Computing 7155/01 1 A bank uses spreadsheet software for computing its loans. Draw a line between the spreadsheet function and its description. Function Description • Calculate the interest payment for a given period PPMT • • Calculate the amount of money to be paid at the end of the loan FV • • Calculate the required interest rate per period of a loan RATE • • Calculate the instalment for a loan PMT • • Calculate the amount of money to be loaned • Calculate the principal payment for a given period [4]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 3 Secondary 4 Express Computing 7155/01 2 A digital clock is controlled by a microprocessor. It uses the 24 hour clock. The hour is represented by an 8-bit register, A, and the number of minutes is represented by another 8-bit register, B. (a) Show how 13:46 can be represented by these two registers. [2] (b) State the hexadecimal representation of the following two registers. Hours (hex) Minutes (hex) [2] (c) State the minimum number of bits that can be used to represent a 24 hour clock Hours bits Minutes bits [2] 3 Program development typically occurs across five distinct stages. (a) List any two stages in developing a program. 1 2 [2] (b) Describe what is “agile” software development. [2]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 4 Secondary 4 Express Computing 7155/01 4 Computers comprise various electronic components and hardware. (a) The table contains hardware commonly used with a computer. Tick () one or more boxes in each row to indicate if the hardware is an input, output or storage device. Hardware Input device Output device Storage device Speakers Processor register Touchscreen monitor Microphone [4] (b) Complete the following table for the types of external storage: Type Example Advantage Disadvantage Optical Large storage capacity of up to gigabytes (GB) of data Lower maximum storage capacity Hard Disk Relatively cheap and large storage capacity of up to terabytes (TB) of data Solid-state More expensive [5]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 5 Secondary 4 Express Computing 7155/01 5 (a) Draw the truth table for a NAND gate. [2 ] (b) An alarm sounds when certain conditions occur in the main reactor of a chemical plant. The output, X of a logic circuit that drives the alarm must have a value of 1 only if: either temperature is high and water level is high in the reactor or water level is low and relief valve is off in the reactor or temperature is low in the reactor The inputs to the system are: Input Binary Condition R 0 Relief valve off 1 Relief valve on T 0 Low temperature 1 High temperature W 0 Water level low 1 Water level high (i) Write down the corresponding Boolean statement for the system. [2] (ii) Draw a logic circuit for the system. [4]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 6 Secondary 4 Express Computing 7155/01 6 Progammers apply a variety of problem-solving techniques. (a) The table shows two scenarios where the decomposition technique is used. Complete the table by stating the approach used in each scenario. Scenario Approach Finding the lowest score in a class test. Take the first score on the list as input and output it as the lowest score for the first sub-problem. The output of the first sub-problem is used together with the second score on the list as inputs to a second sub-problem to output the lowest score. This process goes on until all the scores on the list ha ve been compared, and the lowest score is shown as the final result. Calculating the mean subject grade aggregate . The inputs of the program are individual scores of each subject. The program then separates into two distinct tasks. First task works on the conversion of the scores to grades and the second task sums all the grades and calculate the average grade. The average grade is then shown as the mean subject grade. [2] (b) State two other problem-solving techniques. 1 2 [2]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 7 Secondary 4 Express Computing 7155/01 7 Technology has enabled ease of communication with people all around the world. (a) Describe two economic benefits to businesses using technology. 1 2 [2] (b) Describe one ethical issue of using technology in communication. [1] (c) Organisations are susceptible against cyberattacks like phishing, pharming or spam. (i) Explain the difference between phishing and pharming [2] (ii) Firewalls are commonly deployed in networks. Explain how a firewall works. [2] (ii) Describe one measure to manage spam. [1]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 8 Secondary 4 Express Computing 7155/01 8 Some data are shown in a spreadsheet. Determine the result for the following formulas: =COUNT(A1:H1) =SMALL(A1:H1,2) =MEDIAN(A1:H1) =MODE.SNGL(A1:H1) [4]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 9 Secondary 4 Express Computing 7155/01 9 Computers use a variety of networking devices and identifiers to communicate and exchange data with one another. (a) A laptop requires an IPv6 address, MAC address and SSID to connect wirelessly to other computing devices or the internet. State what IPv6, MAC and SSID represent, what each is used for, and how each can be represented. (i) IPv6 address [3] (ii) MAC address [3] (iii) SSID [3] (b) State two key differences between the functions of a router and a bridge. 1 2 [2] (c) A is used in combination with an IP address to identify a program that is running on a network. [1]

Anglo-Chinese School (Barker Road) Preliminary Examination 2021 10 Secondary 4 Express Computing 7155/01 10 The following pseudo-code represents an algorithm that asks the user to enter a word and stores this in the variable word. It then asks the user to enter the number of letters to be extracted from word in reverse; this number is stored in the variable numLetters. The algorithm extracts the amount of letters the user entered from word, starting with the last letter and then outputs these letters. OUTPUT "Enter a word with more than 3 letters, but less than 10 letters: " INPUT word OUTPUT "Enter the number of letters you want to extract from the reversed word: " INPUT numLetters newWord = revsubstring(word, numLetters) OUTPUT newWord (a) The function revsubstring(theString, numCharacters) returns a number of characters, n