BOON LAY SECONDARY SCHOOL
PRELIMINARY EXAMINATION
2018
Name ( )
Class
Subject : COMPUTING
Paper No : 1
Subject Code : 7155/01
Level : SECONDARY FOUR EXPRESS
Date/Day : 18 SEPTEMBER 2018 (TUESDAY)
Time : 0800 – 1000
Duration : 2 HOURS
Candidates answer on the Question Paper.
No Additional Materials are required.
READ THESE INSTRUCTIONS FIRST
Before you start your exam, check that you have received the correct paper and the
number of printed pages are correct.
Write your name, index number and class 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.
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This document consists of 12 printed pages.
1 A computer system stores and retrieves data from a few types of memory. Name three
types of memory that are commonly found in a computer system and describe each of
them in terms of their speed, size, and/or location.
Type 1…………………………………………………………………………..…………...……
Description……………………………………………………………………..…………...……
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Type 2…………………………………………………………………………..…………...……
Description……………………………………………………………………..…………...……
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Type 3…………………………………………………………………………..…………...……
Description……………………………………………………………………..…………...……
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2 (a) A network is to be setup to allow internet access in the school canteen. Mr
Tan is considering between setting up a wired, or a wireless network.
Describe two differences between wired and wireless networks.
Difference 1…….……………………………………………………..………….....……
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Difference 2…….……………………………………………………..………….....……
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(b) What advantage and disadvantage does wireless networks have compared to
wired networks for the case in part(a)?
Advantage….……………..…………………………………………..………….....……
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Disadvantage……………..…………………………………………..………….....……
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3 The spreadsheet data below shows the contributions of students for a class party.
(a) Write down a formula that will count the number of students who are bringing
more than 2 family members.
= ..…………………………………………………………………………..…...…..…[2]
(b) Write down a formula that has been entered in cell C4 and has been used to
complete the calculation for column Amount. Note that the student will have to
contribute as well.
= ..…………………………………………………………………………..…...…..…[2]
(c) Name the data type for column Name and column Amount.
Data type for Name ……..…………………………………………..………….....……
Data type for Amount …..…………………………………………..………….....…[2]
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4 (a) Write down the largest possible value for a one-byte binary number.
Convert it to a denary number. Show your working.
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(b) Convert the hexadecimal number B3 into a binary number. Show your
working.
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(c) Convert the denary number 26 into a binary number. Show your working.
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5 Unauthorised access occurs whenever data owned by someone is used by someone
else, such as an intruder, or an unknowing individual, without permission.
(a) State two reasons why unauthorised access occurs.
Reason 1...……………………………………………………………..…………...……
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Reason 2...……………………………………………………………..…………...……
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(b) Describe two safety measures to prevent unauthorised access.
Safety measure 1.……………………………………………………..…………...……
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Safety measure 2.……………………………………………………..…………...……
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6 Across the world, the music, television and film industries have been hit hard by acts of
piracy.
(a) Describe two economic effects on the music and film industries if piracy is not
curbed.
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(b) Siti enjoys watching a television series that is only available on an online video
site. After some research, she realises that she can download the television
series onto her computer hard drive so that she can watch the videos without
going online. Explain why her act is considered copyright infringement.
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(c) Describe a situation where music can be downloaded legally without copyright
infringement.
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7 (a) Describe what is meant by data validation in programming.
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(b) Name two common checks that are performed in data validation.
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1.........…………………………………………………………………………..…………
2.........……………………………………………………………………………….…[2]
8 Insert four of the following words about data flow in the correct place in the text below.
an input device an output device processor register
ALU ROM control unit
When using input and output devices, the following data flow may occur.
● The data is entered using …...…………………………...….. and converted into a
form that the computer can understand. This data may be temporarily stored in
a …...…………………………...……
● Instructions from the running application are interpreted by
the …...…………………………...…… These instructions may request the data to be
processed by the …...…………………………...….. .
[4]
9 A shop owner wants to use a computer to find out the bestselling title in 2017. There
were 480 books titles for sale in 2017 and the number of copies sold for each book title
was different.
State the inputs, the outputs and processes required to find the title of the bestselling
book and the number of copies sold for this title.
Inputs.....………………………………………………………………………..…………...……
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Outputs..………………………………………………………………………..…………...……
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Processes required ….…………….………………………………………..…………...……
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10 An algorithm is required to retrieve up to 20 numbers stored from an array and add
them together. It stops reading the data, and output the total when the total exceeds
100. The input is provided in an array called “Number” and the output is provided
through a variable name “Total”.
Study the following pseudo-code.
Total = 100
Counter = 0
WHILE Counter < 20 DO
Number[Counter] + Total = Total
IF Total = 100
Counter = 20
Counter = Counter - 1
ENDIF
OUTPUT Counter
ENDWHILE
There are five errors
OUTPUT oddin this pseudo-code.
Locate the errors and state the correct pseudo- code.
Error 1 ..…………………………………………………………………………..………….…..
Correction…………………………………………………………………………………….…..
Error 2 ..…………………………………………………………………………..………….…..
Correction…………………………………………………………………………………….…..
Error 3 ..…………………………………………………………………………..………….…..
Correction…………………………………………………………………………………….…..
Error 4 ..…………………………………………………………………………..………….…..
Correction…………………………………………………………………………………….…..
Error 5 ..…………………………………………………………………………..………….…..
Correction……………………………………………………………………………………[10]
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11 Identify the logic gates represented by the following truth tables.
(a)
A X
0 1
1 0
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(b)
A B X
0 0 1
0 1 1
1 0 1
1 1 0
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(c) Draw a truth table for an OR gate.
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[2]
11 (d) Two-way switches allow a single light to be switched on or off from two different
locations easily. In the diagram below, light Q at the centre of a long corridor is
controlled by switches A and B at both ends of the corridor.
Each switch has two states: 0 for “off” and 1 for “on”. Light Q also has two states: 0 for
“off” and 1 for “on”. Light Q will be on only when both switches A and B are off or on
concurrently. However, if only one switch is on and the other is off, light Q will be off.
The truth table for the two-way switches is given as below.
A B Q
0 0 1
0 1 0
1 0 0
1 1 1
(i) Write down the Boolean statement for the two-way switch.
………………………………………………………………………………….… [2]
(ii) Draw a logic circuit for the two-way switch.
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[5]
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12 Study the following flowchart.
START
T1 = 0
T2 = 0
T3 = 0
INPUT
A, B, C
Is A = 0 and Yes
B = 0 and OUTPUT END
C = 0? T1, T2, T3
No
Yes Yes T1 = T1 + 1
Is A > B ? Is A > C ?
No
No
Is B > C ? No T3 = T3 + 1
Yes
T2 = T2 + 1
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(a) Complete the trace table for the following set of data.
6, 4, 2 3, 8, 6 5, 0, 2 6, 7, 9 5, 10, 2 0, 0, 0
Trace table
Note that you need not use all the rows given.
T1 T2 T3 A B C OUTPUT
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(b) What is the purpose of the algorithm?
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(c) What is the limitation of the algorithm?
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13 Write an algorithm, using only pseudo-code or a program flowchart, that:
● inputs twenty different numbers between 10 to 999 and stores these number in an
array
● outputs how many numbers of 2 digits and 3 digits value are there
● outputs the sum of all the numbers input
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