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S4 ICT: Data Representation and File Size (Paper 3 (challenge))
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 3 (challenge))
Paper 3 (challenge): 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)
- FoundationAn uncompressed video is 1280 by 720 at 24-bit colour, 25 frames per second, 60 seconds long. How large is it?
- FoundationAn 8 GB drive holds video at 150 MB per minute. How many whole minutes fit?
- FoundationWhat is 11111111 in denary, and how many bits are needed after adding 1?
- IntermediateCD quality audio at 44 100 Hz, 16-bit, stereo, lasts 3 minutes. How large is the uncompressed file?
- IntermediateWhat is the hexadecimal number 1A3 in denary?
- IntermediateA 4 GB file is sent over a 20 Mbps link. Roughly how many seconds does it take?
- ChallengeA 640 by 480 image at 24-bit colour compresses to 60 KB. What is the compression ratio?
- ChallengeEach of the RGB channels uses 5 bits. How many colours can be shown?
- ChallengeHow many 4 MB photos fit on a 1 TB drive?
- Error redoError clinic: a student said 128 kbps means 128 KB per second. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | about 3.86 GB | Each frame is 2 764 800 bytes, so 25 frames over 60 seconds give 4 147 200 000 bytes, about 3.86 GB. |
| 2 | 54 minutes | 8192 MB divided by 150 MB gives 54.6, so only 54 whole minutes fit. |
| 3 | 255; 9 bits | Eight ones give 255, and adding 1 makes 256, which is 100000000, nine bits, so the eight bit register overflows. |
| 4 | 31 752 000 bytes (about 30.28 MB) | Each second holds 44 100 times 2 times 2, which is 176 400 bytes, and 180 seconds give 31 752 000 bytes. |
| 5 | 419 | The place values give 1×256 plus 10×16 plus 3, which is 419. |
| 6 | about 1718 seconds (about 28.6 minutes) | 4 GB is 34 359 738 368 bits, and dividing by 20 000 000 gives about 1718 seconds. |
| 7 | about 15:1 | The original is 921 600 bytes and 60 KB is 61 440 bytes, so the ratio is 15 to 1. |
| 8 | 32 768 colours | Five bits per channel gives 15 bits in total, and two to the power of fifteen is 32 768. |
| 9 | 262 144 photos | 1 TB is 1 048 576 MB, and dividing by 4 MB gives 262 144 photos. |
| 10 | only 16 KB per second | 128 kbps is 128 000 bits, and dividing by 8 gives 16 000 bytes, so bits and bytes differ by a factor of eight. |
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 →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.
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