Logic & Deduction

In this lesson, you will learn how to solve logic and deduction questions. These test your ability to think clearly, follow clues, and work out the answer step by step. They are some of the most challenging — but also the most rewarding — questions in the GL 11+ exam.

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What Are Logic Questions?

Logic questions give you a set of statements (clues) and ask you to work out a conclusion. You might need to:

• Work out who sits where
• Decide what is true or false
• Put things in order
• Match people to items

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Key Thinking Skills

Before we dive into examples, here are the key skills you need:

1. Read carefully — every word matters in a logic question.
2. Use elimination — cross off options that cannot be right.
3. Draw a table or grid — this helps you organise the information.
4. Look for definite facts first — start with clues that tell you something for certain.
5. Work step by step — do not try to solve everything at once.

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Type 1: Ordering / Ranking

Worked Example 1

Question: Read the clues and answer the question.

• Tom is taller than Sam.
• Sam is taller than Alex.
• Alex is taller than Ben.

Who is the shortest?

Step-by-step:

1. From the clues, arrange from tallest to shortest:
   • Tom > Sam > Alex > Ben
2. The shortest is at the bottom.
3. Answer: Ben

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Worked Example 2

Question: Read the clues.

• Priya finished the race before Omar.
• Lucy finished before Priya.
• Omar finished before Dan.

Who came second?

Step-by-step:

1. Lucy finished before Priya, and Priya finished before Omar, and Omar finished before Dan.
2. Order: Lucy, Priya, Omar, Dan.
3. Second place: Priya.
4. Answer: Priya

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Type 2: True or False Statements

Worked Example 3

Question: Read the statement and decide which conclusion must be true.

"All dogs are animals. Some animals are pets."

Which of these must be true?

A) All dogs are pets. B) Some dogs are pets. C) All animals are dogs. D) All dogs are animals.

Step-by-step:

1. "All dogs are animals" — this is stated as fact. So D must be true.
2. "Some animals are pets" — this does not tell us which animals are pets. It could include dogs, but it does not have to.
3. A) "All dogs are pets" — not necessarily true. Some dogs might not be pets (e.g. wild dogs).
4. B) "Some dogs are pets" — this might be true, but it is not guaranteed by the statements.
5. C) "All animals are dogs" — definitely false. There are many animals that are not dogs.
6. D) "All dogs are animals" — this is directly stated.
7. Answer: D

Important: In logic questions, you must pick the answer that must be true based on the information given — not what might be true or what you think is true in real life.

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Type 3: Grid Logic (Matching)

Worked Example 4

Question: Three children — Amy, Ben, and Clara — each have a different pet: a cat, a dog, and a fish. Use the clues to work out who has which pet.

Clues:

1. Amy does not have a cat.
2. Ben does not have a dog.
3. Clara has a cat.

Step-by-step:

Draw a grid:

	Cat	Dog	Fish
Amy
Ben
Clara

From Clue 3: Clara has a cat. Put a tick for Clara-Cat and crosses for Clara-Dog and Clara-Fish. Also put crosses for Amy-Cat and Ben-Cat (since Clara has the only cat).

	Cat	Dog	Fish
Amy	X
Ben	X
Clara	Y	X	X

From Clue 2: Ben does not have a dog. Put a cross for Ben-Dog.

	Cat	Dog	Fish
Amy	X
Ben	X	X
Clara	Y	X	X

Ben has crosses for Cat and Dog, so Ben must have Fish. Put a tick.