Writing Expressions from Truth Tables
Part of Boolean Expressions — GCSE Computer Science
This key facts covers Writing Expressions from Truth Tables within Boolean Expressions for GCSE Computer Science. Revise Boolean Expressions in Boolean Logic for GCSE Computer Science with 15 exam-style questions and 22 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 7 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 7 of 11
Practice
15 questions
Recall
22 flashcards
Writing Expressions from Truth Tables
You can derive a Boolean expression directly from a truth table using the Sum of Products (SOP) method:
Step 1: Find all rows where the output = 1
Step 2: For EACH of those rows, write an AND expression:
- If an input is 1, write it as-is (A)
- If an input is 0, write it with NOT (NOT(A))
Step 3: OR all these AND expressions together
Given: Output is 1 when:
- Row 1: A=0, B=1 → Output=1
- Row 2: A=1, B=1 → Output=1
Step 1: Identify rows with output 1 ✓
Step 2: Write AND expressions for each row:
- Row 1 (A=0, B=1): NOT(A) AND B
- Row 2 (A=1, B=1): A AND B
Step 3: OR them together:
(NOT(A) AND B) OR (A AND B)
Simplified: This actually simplifies to just B (because B is 1 in both cases, regardless of A)