How is this error-review paper different from the first three?

It targets four slips: mixing bits with bytes, ignoring colour depth in bitmaps, dropping audio channels, and reversing the compression ratio.

What is a safe routine for file-size questions?

Convert everything to bits or to bytes first, list each factor (pixels, bit depth, channels, seconds), multiply, and only then convert to MB.

S6 ICT Multimedia and Compression Paper 4: Error Review

2026-11-09

Tutor Prep Guide · S6 ICT

Ten original error-review items, each with an answer and a one-line explanation.

Direct answers　Items 1-3 revisit bitmap size and colour depth, 4-6 cover compression ratio, lossy versus lossless and audio sampling, 7-9 apply bit rate and print resolution, and item 10 separates bits from bytes. Cover the answers first, then check each note.

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: S6 ICT: Multimedia and Compression
Level	S6

02　Questions (10 items)

FoundationError review: how many bytes does an uncompressed 800 x 600 pixel 24-bit colour bitmap need?
FoundationError review: how many bytes per pixel does 24-bit colour use?
FoundationError review: an uncompressed 8-bit greyscale image is 1024 x 768 pixels. How many KiB?
IntermediateError review: a 10 MB file becomes 2 MB after compression. What is the compression ratio?
IntermediateError review: which of these is lossless? A. JPEG B. MP3 C. PNG D. all are lossy
IntermediateError review: uncompressed audio at 44.1 kHz, 16-bit, stereo for 10 seconds needs about how many bytes?
ChallengeError review: how many seconds are needed to download an 8 MB file over a 4 Mbps link (1 MB = 8 Mb)?
ChallengeError review: music compressed at 128 kbps for 4 minutes is about how many MB (1 MB = 8 Mb)?
ChallengeError review: how many pixels are needed to print a 2 inch by 3 inch photo at 300 dpi?
Error redoError review: a pupil claims a 24 MB file takes 1 second at 24 Mbps. What is correct and what went wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	1440000 bytes (about 1.44 MB)	24 bits means 3 bytes per pixel, so 800 x 600 x 3 = 1440000 bytes; multiplying only the pixel count ignores colour depth.
2	3 bytes	24 / 8 = 3 bytes; confusing bits with bytes inflates the file size eight times.
3	768 KiB	8 bits is 1 byte, so 1024 x 768 = 786432 bytes, which is 768 KiB.
4	5 : 1	The ratio is original divided by compressed, 10 / 2 = 5 to 1; writing 1 to 5 reverses it.
5	C. PNG	PNG re-encodes without discarding data, so the decoded image matches the original; JPEG and MP3 throw data away permanently.
6	1764000 bytes	44100 x 2 bytes x 2 channels x 10 s = 1764000 bytes; omitting the channels halves the figure.
7	16 seconds	8 MB is 64 Mb, and 64 / 4 = 16 seconds; treating MB as Mb gives 2 seconds.
8	3.84 MB	128 x 240 = 30720 kb, which is 3840 kB or 3.84 MB; using minutes instead of 240 seconds breaks the sum.
9	600 x 900 = 540000 pixels	Each side is multiplied by 300: 2 x 300 = 600 and 3 x 300 = 900, giving 540000 pixels.
10	8 seconds	24 MB is 192 Mb, and 192 / 24 = 8 seconds; treating bits and bytes as the same unit causes the mistake.

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.

Book an ICT tutor 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.