Ten years ago, she was:
[
50-10=40
]
That's straightforward.
But suppose the question asks how many years have passed since she was 40.
The answer is:
[
50-40=10
]
Not 50.
The numbers may appear together in the story, but they represent different quantities.
This is why careful readers don't simply grab the largest or most obvious number.
## Why People Answer Quickly
There is a psychological reason these puzzles work.
When people encounter a familiar-looking question, they often rely on a mental shortcut called a **heuristic**.
Instead of working through every possibility, the brain searches for the most obvious pattern.
In an ordinary situation, this is efficient.
In a trick puzzle, it's exactly what the puzzle setter wants.
The phrase “Don't make the same mistake!” adds another layer.
It makes the reader anticipate a trap.
Ironically, that can cause people to overthink the problem and choose an unnecessarily complicated interpretation.
The best strategy is neither blind guessing nor excessive suspicion.
