Why do computers use binary?

A circuit has two reliable states, on and off, so 0 and 1 are the safest representation.

What is the difference between KB and KiB?

KB is the decimal prefix of 1000 bytes, while KiB is the binary prefix of 1024 bytes.

S4 ICT Data Representation, Paper 1: binary, hexadecimal and units

2026-11-02

Paper 1 goes from 1011 giving 11, 45 as 00101101, hex 2F giving 47 and one byte being 8 bits, on to 3 bytes as 24 bits, 2 KiB as 2048 bytes, A to D giving 68, 1011 plus 0110 giving 10001 and 5 MiB as 5242880 bytes.

Reminders　Binary place values from the right are 1, 2, 4 and 8, each hex digit is 4 bits, and Ki and Mi are powers of 1024.

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 the binary number 1011?
FoundationWhat is denary 45 in 8-bit binary?
FoundationWhat is the denary value of the hexadecimal number 2F?
FoundationHow many bits are there in one byte?
IntermediateHow many bits are there in 3 bytes?
IntermediateHow many bytes are there in 2 KiB?
IntermediateThe ASCII code of A is 65. What is the ASCII code of D?
ChallengeAdd the binary numbers 1011 and 0110. What is the binary result?
ChallengeHow many bytes are there in 5 MiB?
Error redoError repair: a student said one hexadecimal digit represents 3 bits. How many bits is it really?

03　Answers and one-line notes

#	Answer	One-line note
1	11	One times 8 plus zero times 4 plus one times 2 plus one times 1 gives 8 plus 2 plus 1, which is 11.
2	00101101	45 is 32 plus 8 plus 4 plus 1, so the bits from left to right read 00101101.
3	47	Two times 16 is 32 and F stands for 15, so the total is 47.
4	8 bits	A byte is always 8 bits, so 8 bytes are 64 bits.
5	24 bits	Three times 8 is 24, so three bytes are 24 bits.
6	2048 bytes	The binary prefix Ki means 1024, so 2 KiB is 2 times 1024, which is 2048 bytes.
7	68	Each following letter adds one, and A to D is three steps, so 65 plus 3 gives 68.
8	10001	1011 is 11 and 0110 is 6; 11 plus 6 is 17, which in binary is 10001.
9	5242880 bytes	Mi means 1024 times 1024, which is 1048576, and times 5 gives 5242880 bytes.
10	4 bits	Hexadecimal has 16 symbols and 2 to the power 4 is 16, so each hex digit holds 4 bits.

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.

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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.