When you first look at the math problem, you may think that it is easy. In reality, however, it has been circulating for many years and stumping millions of people along the way. It got its start in Japan.

The problem gained a lot of steam online when a study found that only 60% of those who looked at the question between the ages of 21 and 29 were unable to get it right. That percentage is down from 90% that was seen in the 1980s.

Presh Talwalker of Mind Your Decisions talks about why this relatively simple looking math problem has fooled so many people.

“You should write an expression that groups one third as one group,” he says in the video.

“Three divided by one third is equal to nine, and now we have nine minus nine, plus one,” he added.

Perhaps you may be thinking back to what you learned in school: BODMAS, or brackets, open; divide; multiply; add; and subtract, in that order.

Some people also talk about it as PEMDAS. That acronym stands for parentheses first, exponents (ie powers and square roots) next, multiplication and division (left-to-right), and addition and subtraction (left-to-right).

Are you still with me? How about another?

Here’s another viral math problem:

There were some people on a train.

19 people get off the train at the first stop.

17 people get on the train.

Now there are 63 people on the train.

How many people were there on the train to begin with?

The solution to the problem:

There are 63 people on the train, meaning that one would subtract the 17 people who boarded the train.

Then you would have to account for the 19 people who got off, and one then has to add 19 and 46.

That gives 65, the answer, meaning there were 65 people on the train to start.

Or one could subtract 19 people by 17 people, which equals 2. Then add the other 63 to 2, which equals 65.

Louise Bloxham shared this problem on twitter and an amazing number of people were confused and said that the answer was 46. In reality, that answer only takes the first portion of the problem into account.

A news source stated: “people said that the 19 was a red herring, which doesn’t make sense, or that the train was empty to begin with, which doesn’t make sense. It even says there are ‘some people’ on the train.”

Are Americans bad at math?

It has sometimes been said that Americans are not asking for that matter as people from other developed countries.

“Americans continually score either in the mid- or bottom-tier when it comes to math and science compared to their international peers,” says BigThink. “Students have a fundamental misunderstanding of what math is and what it can do. By viewing it as a language, students and teachers can begin to conceptualize it in easier and more practical ways.”

They say that Americans are too concerned about ‘rote memorization’ and they may have problems understanding concepts in sequential order.

“Unlike the more difficult and comprehensive math tests given to test students’ comprehension, this test was for basic numeracy skills. The United States fell behind in 22nd place,” it says.