Some math problems go viral not because they’re difficult, but because they look easy and trick nearly everyone who tries them.
Today’s puzzle is exactly that kind of trap:
18 + 3 + 4! – 10
Nothing complicated here, right?
Just addition, a subtraction, and a factorial.
Except… when you post this online, you’ll still get a dozen different answers, each defended with total confidence.
Let’s explore the most common answers, why people think that way, and then the actual correct solution.
💠Possible Answer #1: “It’s 15!”
People who get 15 usually treat the equation like a simple left-to-right addition/subtraction problem:
18 + 3 = 21
21 + 4 = 25
25 – 10 = 15
What went wrong?
They treated 4! as just 4 instead of 4 Ă— 3 Ă— 2 Ă— 1.
This happens because factorials aren’t something most people use daily — their brain quickly simplifies them.
💠Possible Answer #2: “It’s 35!”
This one comes from doing the factorial correctly, but then mis-grouping the rest:
4! = 24
18 + 3 = 21
21 + 24 = 45
45 – 10 = 35
The mistake:
They solved correctly but forgot order matters — addition and subtraction must still be done left to right.
Many people assume that once the “big number” from the factorial is found, everything else becomes flexible.
💠Possible Answer #3: “It’s 31!”
This group does most steps correctly, but accidentally combines operations differently:
18 + (3 + 24) – 10
18 + 27 = 45
45 – 14 = 31
The issue:
They add parentheses that don’t exist.
The equation feels long, so the brain naturally clusters it.
It’s a very human mistake — our minds love organizing things even when we shouldn’t.
🧠Why These Mistakes Happen
1. Factorials Aren’t Intuitive
People don’t use factorials often, so when they see “4!”, the brain hesitates —
“Do I do this first? Later? Does it override the left-to-right rule?”
2. People Forget Addition/Subtraction Rules
PEMDAS/BODMAS does not say addition comes before subtraction.
They are equal in priority, so you move left to right.
For many, this memory is fuzzy.
3. Mental Grouping Changes the Equation
Our brain tries to simplify expressions by “chunking” them, even when that changes the math.
âś… Correct Answer
Let’s solve it properly:
Step 1 — Factorial first
4! = 24
Now the equation is:
18 + 3 + 24 – 10
Step 2 — Solve left to right
18 + 3 = 21
21 + 24 = 45
45 – 10 = 35
🎉 Final Answer: 35
Even the cleanest-looking equations can cause chaos when factorials jump in.
This brain teaser is the perfect example of how easy it is to rely on instinct instead of proper order of operations.
