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S4 ICT: Data Representation and File Size (Paper 4 (error clinic))
Tutor Prep Guide · Bits and bytes, the 1024 based KB, MB and GB scale, binary and hexadecimal conversion, ASCII characters, image resolution and colour depth, sound sampling rate and bit depth, video and compression, plus the usual mistakes in file size calculation
S4 ICT: Data Representation and File Size (Paper 4 (error clinic))
Paper 4 (error clinic): ten questions on data representation and file size, with answers and notes.
Direct answers Level: S4 ICT; format: byte conversion, binary and hexadecimal, image and sound file size, compression and unit errors.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 ICT: Data Representation and File Size |
| Level | S4 |
02 Questions (10 items)
- FoundationError clinic: a student wrote that 1 MB equals 1000 KB. What is correct?
- FoundationError clinic: a student said an 8-bit image takes 8 bytes per pixel. What is correct?
- FoundationError clinic: a student read the binary number 1101 as 31. What is the denary value?
- IntermediateError clinic: a student calculated hexadecimal A5 as 105. What is correct?
- IntermediateError clinic: a student got 11 520 000 bytes for an 800 by 600 image at 24-bit colour. What is correct?
- IntermediateError clinic: a student answered 16 000 bytes for one second of 8000 Hz 16-bit stereo. What is correct?
- ChallengeError clinic: a student used the 1000 scale and got 5000 MB for 5 GB. What is correct?
- ChallengeError clinic: a student thought a 128 kbps stream uses 128 KB each second. How many KB is it really?
- ChallengeError clinic: a student said JPEG is lossless. How should it be classified?
- Error redoError clinic: a student wrote 2 000 000 000 bytes for 2 GB. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 1 MB = 1024 KB | The step from KB to MB also uses 1024, while 1000 belongs to the decimal scale. |
| 2 | 1 byte per pixel | Eight bits make one byte, while 8 bytes would be 64 bits, a 64-bit colour depth. |
| 3 | 13 | The place values from left to right are 8, 4, 2 and 1, giving 13, while 31 needs five ones. |
| 4 | 165 | A stands for 10, and 10 times 16 plus 5 gives 165, while 105 comes from skipping the multiply by 16. |
| 5 | 1 440 000 bytes | Multiplying by colour depth only gives bits, so dividing by 8 gives bytes, eight times smaller. |
| 6 | 32 000 bytes | Stereo stores left and right channels separately, so 16 000 must be doubled to 32 000 bytes. |
| 7 | 5120 MB | Converting GB to MB means multiplying by 1024, so 5 GB is 5120 MB. |
| 8 | about 16 KB (15.6 KB) | Dividing 128 kbps by 8 gives 16 KB, because bits and bytes differ by a factor of eight. |
| 9 | JPEG is lossy; ZIP and PNG are lossless | JPEG permanently discards some image data to shrink the file, so the original cannot be fully restored. |
| 10 | 2 147 483 648 bytes | Two times 1024 cubed gives 2 147 483 648 bytes, roughly 147 MB more than the round figure. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Write down the conversion factors first (1 byte = 8 bits, 1 KB = 1024 bytes), then multiply the number of pixels or samples by the bits per unit, and only at the end divide by 8.Tutor Registration →
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