Odd One Out

Odd One Out is a quick, low-prep maths task I love. It engages students, getting them to think and explain their ideas.

How It Works

Give students a small set of numbers, shapes, or data items and let them decide what does not belong. What's great is this sparks discussion and builds critical thinking.

Example 1: Numbers

Which is the odd one out? 2, 15, 24, 36

• 2 → the only single-digit, prime number, not a multiple of 3

• 15 → the only odd number, not divisible by 2

• 24 → the only number divisible by 8

• 36 → the only square number

Example 2: Shapes

Which is the odd one out? Square, Trapezium, Equilateral Triangle

• Square → the only shape with four right angles and two pairs of parallel sides

• Trapezium → the only shape with just one set of parallel sides

• Equilateral Triangle → the only 3-sided shape with equal angles

Each choice could be correct depending on the reasoning!

$Why\; It\text{'}s\; so\; Good$

• Encourages flexible thinking because there’s never just one correct answer

• Boosts students’ confidence in maths by showing that their ideas matter

• Builds mathematical language as students explain and justify their answers

• Works across all areas of maths and can be adapted to any topic

With no prep and endless ways to play, Odd One Out is the perfect warm-up or fast-finisher.