Five Brilliant Brain Teasers For The Week (18/08/25)

Take a breath, grab a scrap of paper, and dive in. Try not to peek at the solutions until you’ve had a good go!

🧠 1. Stamped Out (Easy)

What can travel around the world while staying in the same corner?

🧠 2. Keyed Up (Easy)

I have keys but no locks,

I have space but no rooms,

You can enter but can’t go outside.

What am I?

🧩 3. The Odd One Out (Medium)

You have 9 balls that look identical. One is lighter than the others.

Using a balance scale only twice, how can you find the lighter ball?

🧩 4. Fruitful Deception (Medium)

You have three boxes:

one labeled APPLES,

one labeled ORANGES,

one labeled MIXED.

Each label is wrong. You may draw one fruit from one box (without looking inside beforehand).

How can you correctly relabel all three boxes with that single draw?

🧠💥 5. Checkerboard Conundrum (Hard)

Take a standard 8×8 checkerboard and remove the two opposite corner squares.

Can you cover the remaining 62 squares exactly with 31 dominoes (each domino covers two adjacent squares), or is it impossible? Explain why.

✅ Answers (no peeking next time!)

1) Stamped Out

A postage stamp—it sits in a corner of the envelope and can go around the world.

2) Keyed Up

A keyboard.

3) The Odd One Out

Weigh 3 vs 3.

If one side rises, the lighter ball is among those 3.

If they balance, the lighter ball is among the remaining 3 not weighed.

Second weighing: take the suspect 3 and weigh 1 vs 1.

If they balance, the unweighed one is lighter.

If not, the higher (lighter) one is your odd ball.

4) Fruitful Deception

Draw from the box labelled MIXED (since every label is wrong, this box is not mixed).

Suppose you pull out an apple. Then that box must be APPLES.

The box labeled ORANGES cannot be oranges (labels are wrong) and cannot be apples (already used), so it must be MIXED.

The remaining box (labeled APPLES) must be ORANGES.

(The same logic works if you draw an orange, just swap the roles.)

5) Checkerboard Conundrum

Impossible.

A domino always covers one black and one white square. A full 8×8 board has 32 black and 32 white squares. The two opposite corners are the same colour, so removing them leaves 30 of one colour and 32 of the other—an imbalance. You can’t tile an unequal number of black/white squares with dominoes that always cover one of each.