Subtitle: It sounds simple. It looks simple. But this classic riddle trips up more people than you'd think.

Let me start with a confession.

I love riddles. I love the way they make you pause, rethink, and realize that the obvious answer is almost never the right one. They're little mental puzzles that force you to slow down and think—something most of us don't do nearly enough of these days.

So when I came across this particular riddle, I smiled. It seemed so easy. So straightforward. I was sure I had it figured out in about three seconds.

Then I read it again. And I realized I'd made the exact mistake that trips up 90% of people who try to solve it.

Here's the riddle:

"When I was 2, my sister was twice my age. Now that I'm 40, how old is my sister?"

Seems simple, right? Most people quickly do the math: if the sister was twice as old when the speaker was 2, then the sister must have been 4. That's a 2-year age gap. So now that the speaker is 40, the sister must be 42.

But is that the right answer?

Let's take a closer look.

The Trap: Why Most People Get It Wrong

If you answered 42, you're in the majority. And you're also wrong.

Here's why.

The clue is in the phrasing: "When I was 2, my sister was twice my age."

If the speaker was 2, and the sister was "twice my age," then the sister was 4 years old. That means the sister is exactly 2 years older than the speaker.

Now, here's where people make the mistake. They assume that because the sister was twice the speaker's age at 2, the sister must always be twice the speaker's age. But that's not how age gaps work.

The age gap between two people is constant. It never changes.

If the sister is 2 years older than the speaker, then when the speaker is 40, the sister is 42. That part is correct. But the riddle isn't asking about the age gap—it's asking about the sister's current age.

So why is the answer not 42?

Because the riddle is a trick. It's designed to make you overthink the "twice my age" part. You're so focused on the age gap that you forget to check whether the age gap you calculated is actually correct.