This key facts covers Writing Boolean Expressions from Descriptions within Boolean Expressions for GCSE Computer Science. Revise Boolean Expressions in 3.4 Computer Systems for GCSE Computer Science with 17 exam-style questions and 22 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 5 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Writing Boolean Expressions from Descriptions
You need to translate plain English descriptions into Boolean notation:
| Plain English Description | Boolean Expression | What It Means |
|---|---|---|
| A and B are both true | A AND B | Both inputs must be 1 |
| Either A or B is true (or both) | A OR B | At least one input is 1 |
| A is not true (A is false) | NOT A | A is 0 (inverted) |
| A is false but B is true | NOT(A) AND B | A must be 0 AND B must be 1 |
| A and B, or C | (A AND B) OR C | Either both A&B are 1, or C is 1 |
| Not (A or B) | NOT(A OR B) | Neither A nor B is 1 (both must be 0) |
"Both" or "all" → Use AND
"Either" or "at least one" → Use OR
"Not" or "opposite" → Use NOT
Practice questions for Boolean Expressions
Which Boolean operator produces an output of 1 only when BOTH inputs are 1?
State De Morgan's first law and give an example to illustrate it.