Why is 1.5 KiB not 1500 bytes?

KiB counts in 1024s, so 1.5 times 1024 is 1536, while 1500 belongs to decimal kB.

How do you estimate image size?

Multiply width by height for the pixel count, then multiply by bytes per pixel, with 8 bits equal to 1 byte.

S4 ICT Data Representation, Paper 4: subtraction, capacity and image size

2026-11-03

Paper 4 covers binary 11001 as 25, denary 100 as 01100100, hex 4D as 77, 1.5 KiB as 1536 bytes, 24 bits as 3 bytes, an ASCII gap of 17, 1011 minus 0110 giving 0101, hex A5 as 165, a 640 by 480 greyscale image of 307200 bytes and a hex 1A misread as 11.

Reminders　A hex digit position is worth 16, bits divide by 8 to give bytes, and image size is pixels times bytes per pixel.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S4 ICT: Data Representation
Level	S4

02　Questions (10 items)

FoundationWhat is the denary value of binary 11001?
FoundationWhat is denary 100 in 8-bit binary?
FoundationWhat is the denary value of hexadecimal 4D?
FoundationHow many bytes are there in 1.5 KiB?
IntermediateHow many bytes are there in 24 bits?
IntermediateThe character 0 has ASCII code 48 and A has 65. What is the difference?
IntermediateSubtract binary 0110 from 1011. What is the binary result?
ChallengeWhat is the denary value of hexadecimal A5?
ChallengeA 640 by 480 greyscale image uses 8 bits per pixel. How many bytes and how many KiB?
Error redoError repair: a student evaluated hex 1A as 1 plus 10 equals 11. What is the correct denary value?

03　Answers and one-line notes

#	Answer	One-line note
1	25	Sixteen plus eight plus one is 25.
2	01100100	One hundred is 64 plus 32 plus 4, so those bits are 1 and the rest are 0.
3	77	Four times 16 is 64 and D stands for 13, giving 77 in total.
4	1536 bytes	One KiB is 1024 bytes and half a KiB is 512, which add to 1536 bytes.
5	3 bytes	Every 8 bits make one byte, and 24 divided by 8 is 3.
6	17	Sixty-five minus forty-eight is 17, since digit characters come before capital letters.
7	0101	Eleven minus six is 5, and 5 in four bits is 0101.
8	165	A stands for 10, and 10 times 16 is 160, plus 5 gives 165.
9	307200 bytes, 300 KiB	The pixel count is 640 times 480, which is 307200, and one byte per pixel divides by 1024 to give 300 KiB.
10	26	The leading 1 means one sixteen and A means 10, so 16 plus 10 is 26 rather than a plain digit sum.

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 S4 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.