Complex math problem: can you solve it without making any mistakes?

This calculation seems very simple, almost childish. Yet, it poses a challenge for many adults, because we tend to go too fast and forget the order of operations learned at school.

At first glance, it’s a calculation you could give to a child. A few numbers, plus and minus signs, a multiplication… nothing complicated. And yet, this simple exercise trips up a great many adults. Why? Because we all tend to rush, calculating in the order we read, without thinking about the rules we learned at school. And that’s precisely where the trap lies.

The problem that trips everyone up

Here is the calculation:

15 – 3 × 4 + 6 = ?

Take a few seconds to do it mentally, without a calculator, as if you were in class. Many people find 54, 48, or even 18… when the result is something else entirely. It’s not a problem with the calculation itself, but a problem with the method.

In mathematics, there is a very important rule that is often forgotten over time:  the order of operations .

The order of operations: the rule never to forget

When there are several operations in the same calculation, you don’t calculate from left to right. You must follow a specific order:

Multiplication and division;
addition and subtraction

This means that multiplication must be performed before addition or subtraction, even if it is in the middle of the calculation.

It is this rule that completely changes the result.

Let’s solve the calculation step by step

Let’s go over the calculation again:

15 – 3 × 4 + 6

The first step is to perform the multiplication:

3 × 4 = 12

The calculation then becomes:

15 – 12 + 6

Only now can we calculate from left to right:

15 – 12 = 3
3 + 6 = 9

The final result is therefore 9.

It wasn’t that complicated, but you still had to remember to do the multiplication first.

Why many people are mistaken

 

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 Most errors stem from a natural reflex: reading and calculating from left to right. This makes sense when reading a sentence, but not in mathematics.

Many people do:

15 – 3 = 12
12 × 4 = 48
48 + 6 = 54

This reasoning seems logical, but it doesn’t respect the rules of mathematics. And that’s why the result is wrong.

Over time, we forget some basic rules, especially if we no longer practice mental arithmetic regularly. This kind of short exercise is therefore excellent for training your brain and refreshing your logic.

These little exercises are excellent for the brain

Simple calculations are often underestimated, but they are very useful for stimulating memory, concentration, and logic. Doing these kinds of small exercises regularly helps keep the mind sharp and attentive.

It’s a bit like a mini mental workout: a few calculations, riddles, logic puzzles… and the brain stays active. No need for complicated exercises; sometimes a simple calculation is enough to make us think and test our attention. It’s an excellent  mental math exercise .

So, did you find the right answer?

If you got 9 on the first try, congratulations, you remembered the order of operations correctly. If you made a mistake, don’t worry: it happens to lots of people.

The important thing is not to never make a mistake, but to understand why you made a mistake and to learn to slow down, reflect and check your reasoning before giving an answer.

Because in mathematics, as in life, going slower often allows you to go further.

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