Concept 3 of 7
Odd One Out: Spot the Misfit
Today's big idea
Name the property that exactly three items share, then the fourth is the misfit.
If a second rule fits a different three, the question has two answers, not one.
How it works
👀 What's going on?
Four things sit in a row and one of them does not belong. The catch is that with enough staring you can find a reason to throw out any of the four.
💡 Here's the trick
Look at the row above. The safe move is to name what three of them share, rather than hunting for what one of them lacks. A rule that covers exactly three leaves exactly one misfit standing.
🪄 How to do it
- 1.Read the row above and look for a property three items share.
- 2.State that rule in words before you choose anything.
- 3.Check that no second rule fits a different three.
✍️ Try it
Which is the odd one out among 15, 21, 33 and 35? Then: among 4, 9, 25 and 30?
15, 21 and 33 are all multiples of 3, so 35 breaks the rule. In the second row 4, 9 and 25 are perfect squares, so 30 is the misfit.
⚠️ Watch out
You might be thinking the odd one jumps out first. Work the other way round. Name a rule that fits exactly three, then look for a second rule that fits a different three. If two rules survive, the question has two answers.
🌟 Why this matters
Deciding what a group has in common is how anything gets sorted, from a shelf of books to a folder of photos.
Exam tip: Write the rule down; a rule you cannot say in words is usually not the one intended.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Odd one out: 8, 27, 64, 100, 125.”
- 1
Look for a shared property
8 = 2³, 27 = 3³, 64 = 4³, 125 = 5³ — all perfect cubes.
- 2
Find the misfit
100 = 10 × 10 is a square, not a cube.
- 3
Watch the trap
Don't just pick the biggest (125) — it fits the rule.
- 4
Answer ✓
= 100
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Tap the three that belong together to drop them in the basket. The one left behind is the misfit.
SORT · ROUND 1 OF 3
Quick check
✅ VERIFICATION
Which is the odd one out? 13, 17, 23, 27
⚡ Finish the activity above first to answer.
Keep going!
Up next: Combinations
Every choice pairs with every other → multiply.