Information theory - the big idea: reading answers and analysis
Claude Shannon's information theory, illustrated by NASA's long-distance repair of the Voyager I probe. The passage explains the bit, how noise limits error-free transmission, the coding methods behind Voyager's pictures, bar codes and turbo codes, and how stripping out redundant data allows compression.
The paragraph matching (27-32) uses every paragraph from A to F once, out of order. The notes (33-37) are all in A, in order. The TRUE / FALSE / NOT GIVEN statements (38-40) move from C to E.
Answer key and self-check
Type what you wrote and hit mark. Hide the key first if you haven't done the passage yet. Every question number jumps to its explanation.
Q
Your answer
Answer
Questions 27-32 · Matching information (paragraphs A-F)
How to attack this block: Six items, six paragraphs, one each. Some hinge on a single word: Shannon's attitude to fame is one verb in B. Others describe a whole paragraph, such as the detailed account of the Voyager repair in A.
Question 27
Answer: DParagraph D, middle
Which paragraph explains what affects how information is sent?
This rate depends on the relative strengths of the signal and noise travelling down the communication channel, and on its capacity (its 'bandwidth').
Question says → Passage says
the factors affectingdepends on
the transmission of informationthe rate at which information can pass along communication channels
Why: D lists what the rate of error-free transmission 'depends on': signal strength, noise and bandwidth. Those are the factors.
The trap: C is where Shannon starts thinking about 'how to transmit it from place to place', but C sets the aim. D explains the factors.
Question 28
Answer: FParagraph F, first two sentences
Which paragraph gives an example of cutting out unneeded data?
As mobile phone text messages like 'I CN C U' show, it is often possible to leave out a lot of data without losing much meaning.
Why: 'I CN C U' is the example, and 'leave out' is 'omit'. 'Superfluous' and 'redundant' both mean 'unnecessary'. F.
The trap: E's bar code can be read on a crumpled bag, which sounds like coping with missing data. That's error detection, not deliberately leaving data out.
Question 29
Answer: BParagraph B, middle
Which paragraph shows how Shannon felt about being famous?
While at Bell Laboratories, Shannon developed information theory, but shunned the resulting acclaim.
Question says → Passage says
Shannon's attitude to fameshunned the resulting acclaim
Why: 'Acclaim' is public praise, and 'shunned' means he avoided it. That's his attitude to fame, in B.
The trap: B also has his early talent and gadget-building, which is about Shannon's personality but not fame. Don't miss the single word 'shunned'.
Question 30
Answer: EParagraph E, middle
Which paragraph describes a device that can read data even when some is missing?
a simple error-detecting system that ensures supermarket check-out lasers can read the price even on, say, a crumpled bag of crisps
Question says → Passage says
a machine capable of interpretingsupermarket check-out lasers can read the price
incomplete informationeven on, say, a crumpled bag of crisps
Why: A crumpled bag means the bar code is partly unreadable, yet the laser still reads the price. The laser is the machine. E.
The trap: A's Voyager probe 'managed to hear the faint call', which looks like coping with weak input. But a faint signal isn't incomplete information, and A isn't about how it was read.
Question 31
Answer: AParagraph A
Which paragraph tells a full story of an event involving information theory?
In April 2002 an event took place which demonstrated one of the many applications of information theory.
Question says → Passage says
an incidentan event took place
involving information theorydemonstrated one of the many applications of information theory
Why: A opens by announcing an event and then tells it step by step: the ageing probe, the failing parts, the message, the switchover. That's a detailed account.
The trap: B calls it 'the longest-distance repair job in history', but it only refers back to the event. The details are all in A.
Question 32
Answer: CParagraph C, second sentence
Which paragraph says what Shannon first set out to do?
He set out with an apparently simple aim: to pin down the precise meaning of the concept of 'information'.
Question says → Passage says
initially intended to achieveset out with an apparently simple aim
in his researchthe down-to-earth uses Shannon originally had for his work
Why: 'Set out with an aim' is what he initially intended, and C's first sentence even says 'originally'. C.
The trap: B says he 'single-handedly created an entire science of communication', but that's what he achieved, not what he first planned.
Note completion (NO MORE THAN TWO WORDS)
Questions 33-37
How to attack this block: Everything is in paragraph A, in order. Two gaps need two items each, and both must be there for the mark. Watch the word limit on Q37.
Question 33
Answer: Jupiter and SaturnParagraph A, second sentence
Also accepted: Saturn and Jupiter
Which two planets did Voyager send pictures of?
had sent back spectacular images of Jupiter and Saturn and then soared out of the Solar System
Question says → Passage says
transmitted pictures of bothhad sent back spectacular images of
Why: 'Transmitted pictures' is 'sent back images', and the two planets follow: Jupiter and Saturn, in either order. Both are needed for the mark, and capital letters help.
The trap: Pluto is mentioned later, but only as a point the message passed, not a planet Voyager photographed.
Question 34
Answer: Solar SystemParagraph A, second sentence
What did the probe leave after photographing the planets?
and then soared out of the Solar System on a one-way mission to the stars
Question says → Passage says
then left thethen soared out of the
Why: 'Left' is 'soared out of', and the note's 'then' follows the passage's 'then'. The answer is 'Solar System', two words.
The trap: 'Deep space' comes in the next sentence, but that's where the probe was, not what it left.
Question 35
Answer: sensors and circuitsParagraph A, fourth sentence
Also accepted: circuits and sensors
Which two parts did scientists fear were about to fail?
Sensors and circuits were on the brink of failing and NASA experts realised that they had to do something
Question says → Passage says
Scientists fearedNASA experts realised
were about to stop workingwere on the brink of failing
Why: 'On the brink of failing' is 'about to stop working', and the two things are sensors and circuits. Write both, in either order, and keep them plural.
The trap: 'Parts' and 'spares' are close by but are general words. The question wants the specific components.
Question 36
Answer: sparesParagraph A, fifth sentence
What was the probe told to swap the failing parts for?
The solution was to get a message to Voyager I to instruct it to use spares to change the failing parts.
Question says → Passage says
The only hopeThe solution
tell the probe to replace them withinstruct it to use… to change the failing parts
Why: 'Instruct' is 'tell', and 'use spares to change' becomes 'replace them with spares'. One word answers it.
The trap: 'Failing parts' is what's being replaced, not the replacement.
Question 37
Answer: radio dishParagraph A, middle
What sent the message to Voyager?
By means of a radio dish belonging to NASA's Deep Space Network, the message was sent out into the depths of space.
Question says → Passage says
was used to transmit the messageBy means of… the message was sent out
at the speed of lightEven travelling at the speed of light
Why: 'By means of' tells you what was used. The answer is 'radio dish', two words.
The trap: 'Deep Space Network' is the system the dish belongs to, and it's three words. The note needs the object itself.
TRUE / FALSE / NOT GIVEN
Questions 38-40
How to attack this block: These test whether you can follow Shannon's reasoning in C to E: what came first, what sets the rate limit, and whether anything has beaten that limit.
Question 38
Answer: TRUEParagraph C, middle
Was 'true or false' Shannon's starting point for sending information over distances?
The most basic form of information, Shannon argued, is whether something is true or false… Having identified this fundamental unit, Shannon set about defining otherwise vague ideas about information and how to transmit it from place to place.
Question says → Passage says
the starting pointHaving identified this fundamental unit, Shannon set about
send messages over distanceshow to transmit it from place to place
Why: Shannon first identified true/false (the bit) as the basic unit. 'Having identified' it, he then worked on how to transmit information. So true/false came first: TRUE.
The trap: The statement's wording is quite different from the passage, so people choose NOT GIVEN. 'Having identified… set about' gives you the order you need.
Question 39
Answer: TRUEParagraph D, middle
Do signal strength and noise level decide how much information can be sent in a given time?
The resulting limit, given in units of bits per second, is the absolute maximum rate of error-free communication given signal strength and noise level.
Question says → Passage says
The amount of information that can be sent in a given time periodgiven in units of bits per second, is the absolute maximum rate
determined with reference togiven signal strength and noise level / This rate depends on
Why: Bits per second is an amount over time. The limit is set 'given signal strength and noise level', and the sentence before says the rate 'depends on' them.
The trap: Bandwidth is a third factor, and some students think the missing factor makes it FALSE. The statement doesn't say 'only', so leaving bandwidth out doesn't contradict it.
Question 40
Answer: FALSEParagraph E, last sentence
Do some products now carry more information than Shannon thought possible?
engineers made a major breakthrough by discovering so-called turbo codes - which come very close to Shannon's ultimate limit for the maximum rate that data can be transmitted reliably
Question says → Passage says
more information than Shannon had anticipated as possiblecome very close to Shannon's ultimate limit
Why: Even the best codes, turbo codes, only 'come very close to' Shannon's limit. Close to a limit means not beyond it, and D calls the limit the 'absolute maximum'. FALSE.
The trap: 'Major breakthrough' sounds like going beyond what anyone expected. The key words are 'very close to', and an 'absolute maximum' can't be passed.
'Deep Space Network' is three words and is the system, not the object. The answer is 'radio dish'.
Words from this passage worth keeping
on the brink of(A)
very close to (something bad happening)
shunned(B)
deliberately avoided
acclaim(B)
public praise
inveigled(B)
worked its way in gradually
pin down(C)
define something exactly
ravages(D)
the damaging effects
superfluous(F)
more than is needed
cram(F)
force a lot into a small space
Sit this test on Langujet, then come back
The full Cambridge 9 Test 3 reading paper: all three passages, 60 minutes, marked the second you finish with a review of every answer. Already done it? Take it again and see if the same traps still get you.
Cambridge IELTS 9, Test 3, Reading Passage 3. The passage and questions belong to Cambridge University Press and are not reproduced here. We quote short extracts only as evidence for our own commentary, and the answers are published for self-marking. Get the book for the full text, or sit the test on Langujet.
