Boolean Logic · 5 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 6% of your exam marks.
Writing Boolean expressions from logic diagrams and simplifying using laws appear regularly.
Examiners accept several equivalent notations. Knowing all of them protects against losing marks for "wrong-looking" answers.
| Operator | Word form | Algebraic form | Other accepted forms |
|---|---|---|---|
| AND | A AND B | A · B | AB, A ∧ B |
| OR | A OR B | A + B | A ∨ B |
| NOT | NOT A | ¬A | A̅ (overbar), A' |
| NAND | A NAND B | ¬(A · B) | (A · B)', overbar over the bracket |
| NOR | A NOR B | ¬(A + B) | (A + B)', overbar over the bracket |
| XOR | A XOR B | A ⊕ B | (A · ¬B) + (¬A · B) |
A few important conventions:
· for AND is often dropped, just like in ordinary algebra. So AB means "A AND B", and AB + C means (A AND B) OR C.+ here means OR, not numerical addition. 1 + 1 in Boolean algebra is 1, not 2.¬ or ' instead.A, B, C, ..., with output Q, P, X or Z.Precedence (highest to lowest): brackets → NOT → AND → OR.
This mirrors school algebra: brackets first, then unary −, then ×, then +. As in algebra, brackets remove all ambiguity, so when in doubt, add brackets.
Example — A + B · C reads as A + (B · C) because AND binds tighter than OR. Writing (A + B) · C instead would give a different expression (and a different circuit).