Cambridge IGCSE 0478 · Topic 10 · 10.1

Boolean Logic
& Truth Tables

AND · OR · NOT · Truth Tables · Boolean Expressions

CSZoneCambridge IGCSE Computer Science 0478

AND & OR Truth Tables

Combining Boolean Values

AND

A	B	A AND B
0	0	0
0	1	0
1	0	0
1	1	1

OR

A	B	A OR B
0	0	0
0	1	1
1	0	1
1	1	1

AND: output 1 only when BOTH inputs are 1. OR: output 1 when AT LEAST ONE input is 1.

NOT Truth Table & Boolean Expressions

Inverting & Writing Expressions

NOT

A	NOT A
0	1
1	0

Boolean expressions use letters for variables (A, B, C) and operators:
AND — also written as A · B or AB
OR — also written as A + B
NOT — also written as Ā (A with overline)

Example expression: X = A AND (B OR NOT C) — evaluate from inside brackets first

Truth Table for Combined Expression

Completing a Truth Table

Expression: X = NOT A AND B

A	B	NOT A	X = NOT A AND B
0	0	1	0
0	1	1	1
1	0	0	0
1	1	0	0

Always calculate intermediate columns (e.g. NOT A) before the final output column — shows your working clearly in the exam

Exam Practice

Have a go at this question

Cambridge IGCSE 0478 style

Complete the truth table for the expression: X = (A OR B) AND NOT B

4 marks

A	B	A OR B	NOT B	X
0	0	0	1	0
0	1	1	0	0
1	0	1	1	1
1	1	1	0	0

Key Takeaways

What to Remember

AND: 1 only when BOTH inputs are 1 (like multiplication: 1×1=1 only)

OR: 1 when at least one input is 1 (like addition: 1+0=1, 1+1=1)

NOT: inverts the input — 0 becomes 1, 1 becomes 0

For complex expressions: add intermediate columns to show working; evaluate brackets first