Some of you are probably groaning, “oh no, not math!” For many people, one of the joys of being out of school is that we never have to do an interminable series of problems with the clock ticking in the background.

But as you probably already know, math wasn’t just some absurd hurdle you had to jump over to get your diploma. Try figuring out your insurance, taxes, or even a tip at the restaurant without some basic math skills. You’re not going to get far.

Math is useful in pretty much every area of life from finances to brain training, so try out your wits on the problem below!

Have your answer yet? Seems pretty simple, doesn’t it? Just go from left to right and you’ll get the answer.

First step: 3 + 3 = 6. Pretty easy so far. Then multiply 6 x 3, which gives you 18. If you subtract 3 from 18, you’ll get 15. Add 3 back and you’ll get your final answer: 18. So it’s C, right?

Not so fast. If you did the problem this way, you’ve forgotten a couple of the key principles you learned in math class! If the image of your math teacher scowling at you from across the room is making you sweat and feel queasy, don’t worry; we’ll help you through it.

If you got 18, answer C, then the issue wasn’t your ability to do simple math—the problem was that you didn’t approach the sequence in the correct order.

The problem doesn’t just feature addition and subtraction; there’s a little multiplication too. This means you have to go back to what mathematicians call the “order of operations.” These are rules that tell you what to do first, second, third, etc. when you’re confronted with a problem like the one above.

So, what comes first? Division, then multiplication. After all that’s done, addition then subtraction. Then the final addition. And presto, you’ve got the answer!

Let’s look at our problem one more time. 3 + 3 x 3 – 3 + 3. Keeping in mind the order of operations, let’s do the multiplication first. 3 x 3 = 9. Now if we incorporate that, we get 3 + 9 – 3 + 3.

Sticking with addition, we get 12 (-3) + 3. After subtraction, we have a super simple 9 + 3 = 12. So B is the correct answer after all! How did you do on this challenge? Did you remember the order of operations from school? While this problem was pretty simple, things can get a lot more complicated when you start building up.

Just for fun, let’s keep it going by putting in at twist.

3 + 3 x (3 – 3) ÷ 3. Whoa! What to do? Remember the order: parentheses first, then multiplication and division, and finally addition and subtraction.

If we do the math inside the parentheses, we get 0. This is our multiplier. Can you get the rest from there?

Any luck? Don’t worry if you didn’t get it. Even simple problems like this can be tricky, especially when you’re out of practice like most of us are as adults!

If you follow the order of operations, your work should look something like the tree below:

3+[3×(3−3)]÷3

3+(3×0)÷3

3+0÷3

3+0

What, you’re probably thinking? All of that just to get… 3! That’s right. You had to do all the multiplication and division before adding, which kept the final answer from being 0, as you might have guessed when you started.

Share these brainteasers with your family and friends! Just don’t be surprised if your kids get them before you do.