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MARIS STELLA HIGH SCHOOL
PRELIMINARY EXAMINATIONS
SECONDARY FOUR
COMPUTING 7155
Paper 1 Written 26 August 2020
2 hours
Candidates answer on the Question Paper
No Additional Materials are required.
SOLUTION
For Examiner’s Use
80
2
This document consists of 14 printed pages.
1 Draw a line between the description and the correct spreadsheet function.
Description Function
CEILING
Returns the kth largest number in range
RAND
Returns the largest number out of the
numbers in the given range or cell
references
RANDBETWEEN
Returns a random number greater than or
equal to zero and less than one
HLOOKUP
Rounds up a number to an exact number of
significance
LARGE
Search for data in a row and returns
associated data in the same column.
MAX
[5]
2 (a) A sports event company uses a digital camera attached to a drone to video their
events from the sky.
The video is stored as it is captured, on a device that is attached to the drone.
Circle the most suitable type of media to store the video.
(i) Optical Magnetic Solid State [1]
(ii) Give two reasons to justify your choice.
Three from:
• It has no moving parts so it will be durable as the drone moves/ able to
withstand large impact/ less prone to data loss from shaking/impact
• It is small/compact so it can easily fit onto the device
• It is light so it will not be difficult to lift for the drone
• It can hold a large amount of data needed for the video/film footage [2]
• Uses less power so drone battery will last longer
• Solid state provides faster access/transfer of data than the other two
Comment:
To earn each mark,
state one characteristic of storage media + explain how this characteristic makes it suitable
(1m)
Unacceptable:
Solid state is portable (characteristic stated) but no explanation provided.
3
3 Insert three of the following words about different types of software in the correct place in
each scenario below.
public domain proprietary open
software software courseware
shareware freeware
(a) Ali’s company requires productivity software that can be used in his business for
emailing customers, creating orders, and tracking of the company’s profits and
losses. He would also like regular customer support and updates from the software
company that owns the source code of the software.
The most suitable category of software for this usage is proprietary software
(b) Mingxuan wants to learn more about Python programming during the school
holidays. He wants to enrol for free online lessons provided by a university’s
website that contains videos and training materials for his learning.
The most suitable category of software for this usage is open courseware
(c) Sharon wants to purchase accounting software for her company’s use. She wants
to try out a few features of the software before making a decision whether to
purchase the full version.
The most suitable category of software for this usage is shareware
[3]
4 Five statements about interpreters and compilers are shown in the table below.
Tick ( ü ) to show whether the statement refers to an interpreter or to a compiler.
Statement Interpreter Compiler
√
Translates the entire program in one go.
√
Takes one statement at a time and executes
it.
√
Program runs at a faster speed because
translation was completed earlier.
√
Stops the translation process as soon as the
first error is encountered.
√
Syntax errors are detected before program
runs.
[5]
4
5 (a) Convert the positive whole denary number 388 into a 12-bit binary number.
Divide (398)10 successively by 2 until the quotient is 0:
388 / 2 = 194 with 0 remainder
194 / 2 = 97 with 0 remainder
97 / 2 = 48 with 1 remainder
48 / 2 = 24 with 0 remainder
24 / 2 = 12 with 0 remainder
12 / 2 = 6 with 0 remainder
6 / 2 = 3 with 0 remainder
3 / 2 = 1 with 1 remainder
1 / 2 = 0 with 1 remainder
000110000100
[2]
(b) Convert this binary pattern into hexadecimal.
1 0 1 1 0 0 1 0 1 0 0 1 0 1 1 0
B296
[4]
(c) RGB codes are one example of where hexadecimal numbers are preferred to binary
numbers. Give two reasons to explain so.
• hexadecimal numbers are more compact than binary numbers/ the number of
digits used to represent a given hexadecimal number is fewer than in binary
• uses less storage than binary numbers / a small number of hex digits can
represent more data
• quick and easy to convert between hexadecimal numbers and binary
• easier to identify values using hexadecimal
• easier to spot errors using hexadecimal
[2]
(d) State another two ways in which hexadecimal numbers are used to represent data.
• Colour codes / Colour in HTML / CSS
• Error messages
• Locations in memory
• Memory dump / debugging
• IPv6 address (Unacceptable: IP address, version not stated)
• ASCII / Unicode
• Assembly language
• URL
• M.A.C Addresses
[2]
5
6 Complete the following paragraphs by filling in the missing words about networks.
A local area network is a network of computing devices connected within a small geographical
area, typically within the same building, such as in an office. A wide area network is a network
of computing devices covering across multiple geographical locations, such as those between a
main office in a country and branch offices in other countries.
In an office, there would typically be many client/node computers that initiate connections to
request for resources and services from a centralised computer to perform operations. This
computer which fulfils these requests is known as a server as it centrally manages resources
and services. This type of network is more secure/safe than a peer-to-peer network as access
rights are centrally controlled. X efficient
[5]
7 A program asks the user for a string and prints out the string in reverse order.
For example, “Computing” returns a result of “gnitupmoC”.
For each test case condition below, write down one expected input and one expected
output.
Test Case 1 for Normal Conditions
Expected Input “Apple”
Expected Output “elppA”
Test Case 2 for Boundary Conditions
Expected Input ““
Expected Output “”
Test Case 3 for Erroneous Conditions
Expected Input -50 / “-50” / [1,2,3]
Expected Output Invalid input. A string is expected.
[6]
Comments:
No marks if student leaves out “” (normal conditions)
No marks for single character (boundary conditions)
Message should be meaningful on expected type required. (erroneous condition)
6
8 Personal information needs to be kept safe from unauthorised access.
Explain how the following industries verify personal information.
For each industry, identify the authentication method and explain how it is implemented
to verify user identity.
(a) Online banking services by banks
(i) Authentication Method: Two-factor authentication [1]
(ii) How it is implemented:
Any two:
• Users are issued a security token/device for them to access online
banking OR
• User registers his phone/email address as a 2FA device.
• There are two levels of authentication where user first confirms
identity by providing a secret password or personal identification
number (PIN) to the website
• This is followed by a one-time password (OTP) generated from the
security token or a mobile phone that the user owns, which has to be
keyed into the website
• OTP is single-use only/expires after a short duration
[2]
(b) Passport checking by Immigrations Department
(i) Authentication Method: Biometrics [1]
(ii) How it is implemented:
Any two:
• A user is identified though measuring a physical trait/characteristic
• This characteristic is unique
• Thumbprint or retina eye scan or facial recognition may be used
• Data is matched and checked against a database
[2]
(c) Explain two ways in which a user can protect against unauthorised access of
personal information when using social networking websites.
Any two of the following:
• Read and fully understand the privacy policy of the social networking site.
• Set your sharing settings to ‘private’ so that only people you know in real life
can read your posts.
• Think twice before posting any personal photographs or information that you
may feel uncomfortable sharing.
• Accept friend requests wisely. Make sure you know everyone in your friends
list.
• Set 2FA when logging to social networking websites
• Clear cookies from web browsers regularly
7
• Use secure passwords to prevent unauthorised access / change
password regularly/every 90 days
[2]
Comment:
Some misunderstood the question as unauthorized access of computer
9 A computer has both an IP address as well as a MAC address.
(a) Explain what an IP address is and its function.
Internet Protocol Address
It is used to uniquely identify a device/computer on a network.
……………………………………………………………………………………………...
[2]
(b) Explain what a MAC address is and its function.
Media Access Control
It is used to uniquely identify a network interface card.
……………………………………………………………………………………………...
[2]
8
10 The spreadsheet below contains information about students who registered at a running
club. The ID field is a text that consists of the gender (first character), year of birth (second
to fifth character) and member number (last three characters). Columns C and D are
displayed using data in column B.
(a) Identify the most appropriate data type for the following cell references.
A2 Text
B9 Number [2]
(b) Cells D2 to D7 need to display Year of Birth information using data from column B.
Identify the most appropriate function that will need to be entered in cell D2 using
cell B2.
MID [1]
(c) Cell B9 needs to display the count of students using the cell range B2:B7.
Identify the most appropriate function that will need to be entered in cell B9.
COUNTA [1]
(d) Complete the function used in cell B10 to display the number of female students.
= COUNTIF (C2:C7, “F”)
[2]
(e) Cells C2 to C7 need to have a red background if the cell value has a value of F.
Otherwise, it will have a blue background. State how the cells can be set to
automatically change colour depending on the values inside them.
Conditional formatting
[1]
9
11 The following flowchart shows an algorithm that inputs five temperatures and
outputs the average temperature and the number of temperatures which were
negative.
START
n=0
sum = 0
X=0
count = 1
input T
X=X+1
sum = sum + T
Yes
is T < 0 n=n+1
?
No
count = count + 1
Yes No average = sum/X
is count <= 5?
output
average, n
STOP
10
Complete the trace table for this flowchart using the following test data:
18, 7, 23, –2 , 0
n sum X count T OUTPUT
0
0
0
1
18
1
18
2
7
2
25
3
23
3
48
4
-2
4
46
1
5
0
5
46
6
9.2, 1
[1m] [1m] [1m] [1m] [1m] [1m]
[6]
11
12 (a) Consider the following Boolean statement.
X = NOT (A OR B) OR (NOT (C AND A))
Complete the corresponding truth table.
Working Space
NOT
A B C A OR NOT C AND X
(C AND
B (A OR B) A
A)
0 0 0 0 1 0 1 1
0 0 1 0 1 0 1 1
0 1 0 1 0 0 1 1
0 1 1 1 0 0 1 1
1 0 0 1 0 0 1 1
1 0 1 1 0 1 0 0
1 1 0 1 0 0 1 1
1 1 1 1 0 1 0 0
[4]
(b) Two-way switches allow a single light to be switched on or off from two different
locations easily. In the diagram below, Light R is at the centre of a long corridor,
which is controlled by Switches P and Q at both ends of the corridor.
Each switch has two states: 0 for “off” and 1 for “on”. Light R also has two states:
0 for “off” and 1 for “on”. Light R will be on only when both Switches P and Q are
off or on concurrently. However, if only one switch is on and the other is off, Light
R will be off.
The truth table for the two-way switches is given as below.
P Q R
0 0 1
0 1 0
1 0 0
1 1 1
Write down the Boolean statement for the two-way switch.
R=
Any one below:
(P AND Q) OR (NOT P AND NOT Q)
(P AND Q) OR (P NOR Q)
(P AND Q) OR (P NAND Q)
NOT (P XOR Q)
[2]
12
(c) Draw a logic circuit to represent the following Boolean statement. Do not
simplify the statement.
X = NOT (A OR B) OR (NOT (C AND A))
[5]
13
13 The Elections Department is using a computer program to read in the ages of 100 citizens
and then outputs the results based on the conditions below. Each age is a whole number
greater than 0. You must validate this input.
Write an algorithm, using only pseudo-code or a program flowchart that takes the ages of
100 citizens as input and then
• outputs the count of eligible voters who are aged 21 or above.
• outputs the count of non-eligible voters.
• outputs the average age of an eligible voter.
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[9]
14
13 Flowchart
START
eligible = 0 [1]
non_eligible = 0
count = 0
totalage = 0
average = 0
OUTPUT “Enter an age”
INPUT age [1]
No
Is age > 0? [2]
Yes
No
Is age >= 21? non_eligible =
[1]
non_eligible + 1
[1]
Yes
eligible = eligible + 1 [1]
totalage = totalage + age [1]
[1]
count = count + 1
[1]
Yes
Is count < 100?
No
average =
totalage / eligible [1]
OUTPUT “No of eligible voters:’, eligible
OUTPUT “No of non-eligible voters:’, non-eligible
OUTPUT “Average age:’, average [1]
END
15
[9]
Pseudo-code
eligible = 0
non_eligible = 0
count = 0
totalage = 0
average = 0
WHILE count < 100
REPEAT UNTIL
OUTPUT “Enter an age”
INPUT age
age > 0
IF age >= 21
eligible = eligible + 1
totalage = totalage + age
ELSE
non_eligible = non_eligible + 1
ENDIF
count = count + 1
ENDWHILE
average = totalage / eligible
OUTPUT “Count of eligible voters: “ + eligible
OUTPUT “Count of non-eligible voters: “ + non-eligible
OUTPUT “Average age of eligible voter is: “ + average
Total [9]
IMPORTANT NOTE:
• Before INPUT, there should be a meaningful OUTPUT message to inform user
on the type of input required.
• OUTPUT should comprise of message that indicates the type of variable
printed,
i.e. OUTPUT “Count of eligible voters: “ + eligible (CORRECT)
i.e. OUTPUT eligible (INCORRECT)
-End of Paper-
