Easy-looking math equation mystifies people as they forget 'special rule' - can you solve it in 30 seconds?
A back-to-basics brain teaser is dividing the internet.
BholanathDutta shared the sum 100 + 100 × 4 = ? on X, formerly Twitter, sparking debate among users.
At first glance, many people speed to the wrong answer because they add before they multiply.
It's the kind of thing you might expect to knock out in seconds without even thinking.
But that's exactly where so many people slip up.
In the rush to solve it, countless would-be problem solvers go straight from left to right.
That leads them to add 100 and 100 first, then multiply the result by four - confidently shouting 800.
Unfortunately, that's not how math class taught us to do it. There's a 'special rule' most of us learned years ago but have long since forgotten - the order of operations.
The viral chalkboard challenge: 100 + 100 × 4 = ?
At first glance, many people speed to the wrong answer because they add before they multiply.
But the 'special rule' here is the order of operations PEMDAS: parentheses first, then exponents, multiplication and division, and finally addition and subtraction.
The correct solution:
Do the multiplication first.
100 × 4 = 400
Then add the remaining 100.
100 + 400 = 500
Why people get it wrong: racing the clock, some treat it like (100+100)×4 and shout 800.
Answer revealed: following the order of operations gives 500, not 800
Without parentheses, that’s not allowed - multiplication must come before addition.
If there are no brackets, handle × and ÷ left to right before + and −.
Only group numbers if parentheses/brackets tell you to.
