# Information theory - the big idea: answers and explanations

Cambridge IELTS 9, Test 3, Reading Passage 3

Source: Passage, questions and answer key from Cambridge IELTS 9, Test 3, Reading Passage 3. © Cambridge University Press & Assessment. Used for educational practice. Explanations and evidence notes are written by Testmigo.

## Answer key

| Q | Answer | Proof |
| --- | --- | --- |
| 27 | D | This rate depends on the relative strengths of the signal and noise travelling down the communication channel, and on its capacity |
| 28 | F | 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. |
| 29 | B | Shannon developed information theory, but shunned the resulting acclaim |
| 30 | E | ensures supermarket check-out lasers can read the price even on, say, a crumpled bag of crisps |
| 31 | A | In April 2002 an event took place which demonstrated one of the many applications of information theory. |
| 32 | C | He set out with an apparently simple aim: to pin down the precise meaning of the concept of 'information'. |
| 33 | Jupiter and Saturn | had sent back spectacular images of Jupiter and Saturn |
| 34 | Solar System | soared out of the Solar System on a one-way mission to the stars |
| 35 | sensors and circuits | Sensors and circuits were on the brink of failing |
| 36 | spares | to instruct it to use spares to change the failing parts |
| 37 | radio dish | By means of a radio dish belonging to NASA's Deep Space Network |
| 38 | TRUE | 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. |
| 39 | TRUE | the absolute maximum rate of error-free communication given signal strength and noise level |
| 40 | FALSE | which come very close to Shannon's ultimate limit for the maximum rate that data can be transmitted reliably |

## Why these answers are right

**27. D.** The item wants an explanation of what affects how information is transmitted. Paragraph D says the error-free rate depends on the relative strengths of signal and noise and on the channel's capacity, or bandwidth. Those are the factors, so D is correct.

**28. F.** The item asks for an example of leaving out unnecessary information. Paragraph F discusses stripping out redundant bits and gives text messages such as I CN C U, which drop letters yet keep their meaning, so the example is in F.

**29. B.** You need a mention of Shannon's attitude to fame. Paragraph B says that at Bell Laboratories he developed information theory but shunned the resulting acclaim. Shunning acclaim means avoiding praise and celebrity, so paragraph B holds the reference to how he felt about fame.

The why and the trap for questions 30 onwards are free with an account on the [answers page](https://testmigo.com/ielts/reading/information-theory-the-big-idea/answers).

[Practice Information theory - the big idea](https://testmigo.com/ielts/reading/information-theory-the-big-idea)