MskProdComputing
Time left25:00 Answered 0 of 14 25 marks
MskProd Year 9 unit exam 25 minutes 25 marks Original paper

Data Representation: Unit Exam B

More conversions between binary, denary and hexadecimal, binary addition, colour depth, sound file sizes, ASCII and Unicode.

Instructions

Time allowed
25 minutes
Total marks
25
Calculator
No calculator is permitted.
  • Answer all the questions.
  • The number of marks for each question is shown in brackets. Use it as a guide to how much to write.
  • The clock at the top counts down from the real time allowed. When it reaches zero the paper is locked and marked, as it would be collected in the exam hall.
  • Read every question to the end before answering. Where a question says tick two boxes, tick exactly two: ticking more than asked scores nothing. Type one word and number answers carefully, because they are marked exactly.

Questions

Answer every question, then finish the paper to have it marked. Marking as you go teaches you far less.

25 marks
1Convert each 8-bit binary number to denary.3 marks

Mark scheme0 / 3
  • L102
  • L153
  • L127
Model answer

0110 0110 = 64 + 32 + 4 + 2 = 102. 1001 1001 = 128 + 16 + 8 + 1 = 153. 0111 1111 = 127.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
2Convert each denary number to an 8-bit binary number.2 marks

Mark scheme0 / 2
  • L00010010
  • L11111111
Model answer

18 = 16 + 2 = 0001 0010. 255 is every bit set: 1111 1111.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
3Convert each hexadecimal number to 8-bit binary.2 marks

Mark scheme0 / 2
  • L01111110
  • L11000100
Model answer

7 is 0111 and E is 1110: 0111 1110. C is 1100 and 4 is 0100: 1100 0100.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
4Convert each denary number to hexadecimal.2 marks

Mark scheme0 / 2
  • L1F
  • LA0
Model answer

31 = 1 x 16 + 15, so 1F. 160 = 10 x 16 + 0, so A0.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
5Add these two 8-bit binary numbers. Give your answer in binary.0011 1001 + 0101 01011 mark

Mark scheme0 / 1
  • L10001110
Model answer

57 + 85 = 142, which is 1000 1110.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
6Tick one box in each row.4 marks
TrueFalse
The largest number that 8 bits can hold is 255
Hexadecimal uses the digits 0 to 9 and the letters A to F
Adding two 8-bit numbers can never cause overflow
A nibble is half a byte

Tick one box in each row.

Mark scheme0 / 4
  • LThe largest number that 8 bits can hold is 255: True
  • LHexadecimal uses the digits 0 to 9 and the letters A to F: True
  • LAdding two 8-bit numbers can never cause overflow: False
  • LA nibble is half a byte: True
Model answer

255 is 1111 1111. Hex has sixteen digits. Two 8-bit numbers can add up to more than 255. A nibble is 4 bits.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
7How many different colours can be shown with a colour depth of 3 bits?1 mark

Mark scheme0 / 1
  • L8
Model answer

2 x 2 x 2 = 8.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
8What is the smallest colour depth that can show 16 different colours?1 mark

Mark scheme0 / 1
  • L4 bits
Model answer

2 to the power 4 is 16, so 4 bits.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
9A sound is recorded for 10 seconds at 1000 samples per second, with a bit depth of 8 bits. Calculate the file size in bytes. Show your working.3 marks

Mark scheme0 / 3
  • LCorrect answer, full marks: 10000 bytes
  • LMethod: Multiplies the time by the sample rate
  • LMethod: Multiplies by the bit depth, then divides by 8 to turn bits into bytes
Model answer

10 x 1000 = 10,000 samples. 10,000 x 8 bits = 80,000 bits. 80,000 / 8 = 10,000 bytes.

The marker looks for key phrases. If you said it another way and it is still right, give yourself the mark.
10Which change makes a sound recording more accurate?1 mark

Tick one box.

Mark scheme0 / 1
  • LC Increasing the bit depth
Model answer

A greater bit depth records each sample more precisely.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
11Explain the difference between ASCII and Unicode.2 marks
Explain

Mark scheme0 / 2
  • LASCII uses 7 or 8 bits per character, so it has only 128 or 256 characters, mainly English
  • LUnicode uses more bits, so it can represent far more characters, including every language and emoji
Model answer

ASCII uses 7 bits per character, giving 128 characters: enough for English letters, digits and punctuation but little else. Unicode uses more bits per character, so it can represent over a million characters, covering every writing system and emoji.

The marker looks for key phrases. If you said it another way and it is still right, give yourself the mark.
12What is the resolution of an image?1 mark

Tick one box.

Mark scheme0 / 1
  • LD The number of pixels, given as width by height
Model answer

Resolution is the image's size in pixels, such as 1920 x 1080.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
13How many bits are in 3 bytes?1 mark

Mark scheme0 / 1
  • L24
Model answer

3 x 8 = 24.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
14In ASCII, a is 97. What is the code for d?1 mark

Mark scheme0 / 1
  • L100
Model answer

d is three letters after a: 97 + 3 = 100.

Marked exactly against the mark scheme. Change it only if an examiner would accept your answer.
Machine mark 0 / 25
About this paper

This is an original Key Stage 3 assessment. Most questions are closed, so the marking is exact, and the written answers are marked against a mark scheme in the same style as a GCSE paper, so the format is familiar long before it counts.