Oxford AQA IGCSE · Computer Science (9210)

Data compression: Practice Questions

4 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Data compression.

9 questions24 marksFree, no account

Question 1

1 mark

Why is data compression frequently used when storing or transmitting files over a network?

Question 2

1 mark

A short text document takes up \(700\) bits of space when stored using \(7\)-bit ASCII. After applying Huffman coding, the file size is reduced to \(380\) bits. How many bits have been saved through compression?

Question 3

1 mark

In a Huffman tree, the following character codes are assigned:
- 'E' is represented by \(0\)
- 'T' is represented by \(10\)
- 'A' is represented by \(11\)

What is the binary representation of the word 'TEA' using these codes?

Question 4

1 mark

A row of pixels in a black and white bitmap is represented by the binary string: 0000111000000. Which of the following represents this data using Run Length Encoding (RLE) frequency/data pairs?

Question 5

2 marks

Explain one reason why it is often necessary or desirable to use data compression when storing files on a computer.

Write your answer out first, then check it against the worked solution.

Question 6

3 marks

Use Run Length Encoding (RLE) to represent the following binary data as frequency/data pairs:
00000011100000

Write your answer out first, then check it against the worked solution.

Question 7

6 marks

A message contains the characters 'AAAAABCC'. Calculate the total bits required using 7-bit ASCII and determine how many bits are saved if Huffman coding is used with the following codes: A=0, B=10, C=11.

Write your answer out first, then check it against the worked solution.

Question 8

4 marks

Run Length Encoding (RLE) is a form of lossless data compression.
Part A: Explain the purpose of data compression in computer systems.
Part B: A row of pixels in a simple bitmap is represented by the following binary string:
000000111111110000
Represent this data using RLE frequency/data pairs as specified in the syllabus.

Write your answer out first, then check it against the worked solution.

Question 9

5 marks

The following Huffman tree is used to encode a message containing the characters A, B, C, and D.
- The path to A is 0
- The path to B is 10
- The path to C is 110
- The path to D is 111

Part A: Decode the following bitstream using the tree: 110010111.
Part B: Calculate how many bits would be required to store the string "ABACAD" using this Huffman tree.
Part C: Calculate the number of bits required to store the same string "ABACAD" using standard 7-bit ASCII.

Write your answer out first, then check it against the worked solution.

* The content provided by thinka is generated by AI and may not always be accurate or up-to-date. Please use it as a supplementary resource and verify with official materials.

You've seen the model answer. Now get yours marked.

This page can show you how a good answer looks. It cannot tell you what your answer was missing. thinka marks your written work against the real mark scheme in about 15 seconds.

Get My Answers Marked Back to the notes

Want more questions like these? Get a fresh set on this topic, marked as you go.