What is a truth table?

A truth table lists every possible combination of inputs with the output each one produces. The table shows how a logical expression behaves in every case.

In a truth table, what do 1 and 0 stand for?

The value 1 stands for True and 0 stands for False. Truth tables often use 1 and 0 because they are quick to write.

State how many rows a truth table with three inputs needs, and explain why.

A three-input truth table needs 8 rows. Each input can be 0 or 1, giving 2 × 2 × 2 = 8 combinations.

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Computational Thinking

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Computational Thinking

Truth tables

3 things to know
Paper 1

Overview

AND, OR and NOT, truth tables with up to three inputs, worked values of combined expressions, and alarm and heating problems solved with logic.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What does the AND operator output?

Key term

What does the OR operator output?

Key term

Describe the effect of the NOT operator.

Questions from this subtopic

Each one with the model answer underneath.

1
What does the AND operator output?
Model answer
The AND operator outputs True only when both inputs are True. Any False input makes the output False.
2
What does the OR operator output?
Model answer
The OR operator outputs True when at least one input is True. The output is False only when every input is False.
3
Describe the effect of the NOT operator.
Model answer
The NOT operator inverts a single input. True becomes False and False becomes True.
4
What is a truth table?
Model answer
A truth table lists every possible combination of inputs with the output each one produces. The table shows how a logical expression behaves in every case.
5
In a truth table, what do 1 and 0 stand for?
Model answer
The value 1 stands for True and 0 stands for False. Truth tables often use 1 and 0 because they are quick to write.
6
State how many rows a truth table with three inputs needs, and explain why.
Model answer
A three-input truth table needs 8 rows. Each input can be 0 or 1, giving 2 × 2 × 2 = 8 combinations.

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