This math riddle is driving adults crazy — can you figure it out?

At first glance, it looks like a simple math sequence — until the numbers start breaking the rules. This riddle has gone viral for a reason: it tests your ability to spot hidden logic, not just add numbers.

Here’s the puzzle:

• 1 + 4 = 5
• 2 + 5 = 12
• 3 + 6 = 21
• 8 + 11 = ?

The first line seems right. But what happens next makes no sense — unless you figure out the trick behind the pattern.

According to this report published by Pravda.ru, this riddle is less about math skills and more about logical creativity.

What seems obvious — and what’s actually happening

Common mistake — and why it happens

• Mistake: assuming standard addition
  Why we fail: the brain defaults to learned rules and ignores alternate logic
• What’s really happening: each line adds the previous result to the current sum

FAQ — what people ask

• Is there only one right answer? There are alternate solutions, but this is the cleanest pattern
• Is it a trick? Not really — it’s a cognitive flexibility test
• Why do puzzles like this matter? They reveal how quickly we fall into automatic thinking

Fun fact: puzzles like this are used in job interviews to test creative logic — it’s not about getting the “right” answer, but about how you approach unexpected patterns.