Pearson Edexcel · GCSE · Computer Science
Course version: 1CP2 · Version from Sept 2020
Be able to apply logical operators (AND, OR, NOT) in truth tables with up…
Full specification wording
Truth tables: 1.3.1 be able to apply logical operators (AND, OR, NOT) in truth tables with up to three inputs to solve problems *In this specification, the term ‘pseudocode’ is used to denote an informal written description of a program. Pseudocode uses imprecise English language statements and does not require any strict programming syntax.
A truth table lists every combination of input values and the output for each combination.
Checked against the Pearson Edexcel 1CP2 specification (opens in a new tab) on .
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A truth table lists every combination of input values and the output for each combination. With three inputs there are 2³ = 8 rows, so list them systematically, for example A, B and C counting in binary from 000 to 111. AND gives 1 only when both operands are 1; OR gives 1 when at least one operand is 1; NOT reverses a single value. Work out the expression in stages: evaluate the bracketed part first, then combine the results. For example, with A = 1, B = 0 and C = 1, the expression (A AND B) OR NOT C gives (1 AND 0) OR NOT 1, which is 0 OR 0, so the output is 0. Check each row independently and keep the column headings clear. Pseudocode in this specification is an informal written description using imprecise English statements and does not require strict programming syntax.
What earns the marks
- Identifies that a truth table with three inputs has 2³ = 8 rows and lists all input combinations without repetition or omission.
- Applies AND correctly, producing 1 only when both operands are 1.
- Applies OR correctly, producing 1 when at least one operand is 1.
- Applies NOT correctly, reversing a single input or sub-expression value.
- Evaluates a compound expression in the correct order, working out bracketed or NOT parts before combining with AND and OR.
- Reads the completed table to answer the problem, for example identifying the input combination that produces a given output.
Common mistakes and how to put them right
Missing rows in a three-input table.
Put it right: There are 2³ = 8 rows, so list all combinations from 000 to 111 systematically.
Treating OR as exclusive, so that 1 OR 1 is marked 0.
Put it right: OR gives 1 when at least one operand is 1, so 1 OR 1 gives 1.
Applying NOT to the whole expression when it applies only to one variable.
Put it right: Check what the NOT symbol or word is attached to before reversing a value.
Evaluating left to right without regard to brackets.
Put it right: Work out bracketed sub-expressions and NOT terms first, then combine with AND and OR.
Exam tips
- Write the input columns in a fixed order such as 000, 001, 010 and so on, so no combination is missed.
- Add intermediate columns for sub-expressions; this reduces errors and can earn method credit.
- Recheck each row by substituting the values back into the original expression before selecting your answer.
Try the lesson
The start of the Truth tables: 1.3.1 be able to apply logical operators (AND, OR, NOT) in truth tables with up to three inputs to solve problems *In this specification, the term ‘pseudocode’ is used to denote an informal written description of a program. Pseudocode uses imprecise English language statements and does not require any strict programming syntax. lesson, made from checked teaching notes for this specification point.
Have a go first
A pseudocode condition is IF raining AND cold THEN take a coat. Let A = 1 mean it is raining and B = 1 mean it is cold. Give the output of A AND B for the four input combinations 00, 01, 10 and 11, in that order.
Listen
A truth table lists every combination of input values and the output for each combination. With three inputs there are 2³ = 8 rows, so list them systematically, for example A, B and C counting in binary from 000 to 111. AND gives 1 only when both operands are 1; OR gives 1 when at least one operand is 1; NOT reverses a single value. Work out the expression in stages: evaluate the bracketed part first, then combine the results. For example, with A = 1, B = 0 and C = 1, the expression (A AND B) OR NOT C gives (1 AND 0) OR NOT 1, which is 0 OR 0, so the output is 0. Check each row independently and keep the column headings clear. Pseudocode in this specification is an informal written description using imprecise English statements and does not require strict programming syntax. A strong answer earns marks for these points. Identifies that a truth table with three inputs has 2³ = 8 rows and lists all input combinations without repetition or omission. Applies AND correctly, producing 1 only when both operands are 1. Applies OR correctly, producing 1 when at least one operand is 1. Applies NOT correctly, reversing a single input or sub-expression value. A common slip: Missing rows in a three-input table. Instead, there are 2³ = 8 rows, so list all combinations from 000 to 111 systematically. Exam tip: Write the input columns in a fixed order such as 000, 001, 010 and so on, so no combination is missed.
See it
Put it in order
Put these steps in the order they happen.
- 1. Evaluate NOT terms
- 2. Evaluate bracketed part first
- 3. List all input combinations: 2³ = 8 rows, 000 to 111
- 4. Read completed table to answer the problem
- 5. Check each row independently
- 6. Combine results with AND and OR
Key words
Say what each word means before you turn the card.
Truth table
Try answering aloud or in your head before turning the card.
AND
Try answering aloud or in your head before turning the card.
OR
Try answering aloud or in your head before turning the card.
See every definition
- Truth table
- Lists every combination of input values and the output for each combination.
- AND
- Gives 1 only when both operands are 1.
- OR
- Gives 1 when at least one operand is 1.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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Test your understanding of Truth tables: 1.3.1 be able to apply logical operators (AND, OR, NOT) in truth tables with up to three inputs to solve problems *In this specification, the term ‘pseudocode’ is used to denote an informal written description of a program. Pseudocode uses imprecise English language statements and does not require any strict programming syntax.
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