OCR Computer Science for A Level
Teaching and Learning Resources
Chapter 2: Elements of computational thinking
ANSWERS TO QUESTIONS IN THE STUDENT’S BOOK
Page 22
Questions
Given a regular traffic hold-up spot at a junction:
1. What data would you need to acquire?
2. What processes to solve the problem might you consider?
3. To what extent do you think the problem is intractable?
Answers
1. Examples: number of vehicles … at different times, speed of vehicles … per unit time,
time stationary … at different times.
2. Examples: install traffic lights if not there already, change traffic-light phasing, install
roundabout, major re-work to junction such as flyover.
3. Discussion – no right answers but consider: traffic density may be beyond management
solutions; may be related to other issues beyond road planners’ control; if no good
public transport, maybe that is beyond road-management control. However, some
mitigation may be possible.
Question
Your mobile phone is normally fine. It doesn’t work today. Explain how you could use backtracking
to find what the problem is.
Answer
Depends on the problem but essential strategy is to try a sequence of fixes such as:
·
·
·
·
·
check coverage
if insufficient, try another location
if no fix then try another approach such as check network settings
if they are ok then backtrack
else fix then move on, etc.
Page 25
Question
Itemise some of the inputs, outputs and processes involved in building a house.
Answer
There are various possibilities here but consider in particular which processes need to be
in succession and which ones can proceed simultaneously.
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Page 26
Question
1. Suggest ways to use computing techniques to visualise data about:
(a) the age of people living in different parts of a city
(b) the means of transport used to get from the suburbs into a city centre.
Answer
There are no limits to the ways in which your creativity can be applied to these two
questions so there are no definitive right answers. Consider how large amounts of data can
be simplified into striking visual images.
(a) At its simplest, you could superimpose pie charts over a map. Try looking here for
more ways: www.datavizcatalogue.com/search/distribution.html.
(b) Lines of different thicknesses could show on a diagrammatic map the popularity of
modes of transport.
Question
2. In each case, suggest what data would be needed, how it could be collected and whether there
is existing software to do the visualisation.
Answer
Again, this is an open-ended question with no definitive answers. It may be that data
already exists to help these applications, in which case collecting it may be less onerous
than you might think.
Questions
Read the example scenario.
1. Itemise information from this description that would be of use in finding the missing phone.
2. Suggest a strategy for finding the phone.
3. Suggest a sequence of steps that would be helpful in finding the phone.
Answers
1. Make, model, possibly ringtone if it is switched on, location of where last seen, contact
details of taxi firm.
2. Could try one strategy after another, then use backtracking for failed attempts.
3. Depends on choice of method. Could work through each strategy from start to finish, or
could apply a holistic approach to judge quickly the most likely successful outcome.
Page 27
Question
1. Explain how a map is an example of an abstraction.
Answer
A map is a representation of reality. It uses symbols to transfer real world to paper.
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Question
2. Identify examples of levels of abstraction on a map of your choice.
Answer
Depends on map chosen. A good example is the London Underground map where
distances and real world locations are sacrificed in order to make getting around
successfully the top priority; use of colour to indicate lines; symbols to represent
interchange stations.
Question
3. Explain how levels of abstraction assist the map-maker.
Answer
Allows attention to the purpose of the map and its usability. Unnecessary detail can be
omitted.
Question
4. Explain how levels of abstraction assist the map user.
Answer
Similar to above – the usability is the priority. Maps can be specialised for a purpose such
as travel or geological study.
Page 28
Question
Explain in detail how prefetching is useful when:
(a) baking a cake
(b) cleaning a car.
Answer
In each case performance is improved by having the resources ready to avoid interrupting
the main task.
Prefetching is useful in processing program instructions because it speeds up the execution
of the program. Anticipated instructions are fetched before they are needed and placed in a
cache from which they can be obtained quickly, so that there is no delay in accessing the
slower RAM.
This is analogous to non-computing tasks that involve processing stages one after another
such as baking a cake or washing a car. If the anticipated resources are made available
before processing, there is less waiting to get hold of them when they are needed.
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Page 29
Question
Outline some problems and sub-problems that would form a plan for producing a multi-player
online game.
Answer
Examples: Need to consider number of (simultaneous) players, bandwidth requirements,
processor requirements and likelihood of players having computers of sufficient spec,
costs, income – how to monetise it.
Page 30
Question
In each of these scenarios, is the order of solution important? For each case, list some of the main
sub-problems in a sensible order. Are there any steps where the order does not matter?
1. Building a house.
2. Buying a train ticket online.
3. Buying a drink in a coffee shop.
Answer
This is an open-ended question – no specific answers can be supplied. Consider whether
the efficiency of each scenario would be much affected by poor planning.
Page 31
Question
1. Devise a visual representation of how your computing project could be planned over a
designated time period.
Answer
You could produce a Gantt chart or similar using project-management software of a
spreadsheet.
Question
2. You have lost your wallet on the way to school or college. Explain how backtracking can help
you find it.
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Answer
Go to the last place where you could have dropped it. If it's not there, go back to the
previous place, etc.
Question
3. Draw a flowchart to show how an email address could be validated as being in the correct
format.
Answer
Suggested start – could add further checks:
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015
OCR Computer Science for A Level
Teaching and Learning Resources
Question
4.
(a) Explain what pipelining is.
(b) Show how pipelining can be used to improve the efficiency of a self-service cafeteria.
Answer
(a) Pipelining is a set of processes connected in series. The output of one is the input of
the next.
(b) Assume that a number of items are required, such as cup, coffee, milk, sugar, etc.
Arrange so that common choices are able to be processed in an order that makes
sense, for example put the cups at the entrance.
OCR Computer Science for A Level Chapter 2
© Hodder & Stoughton Limited 2015