A math question apparently meant for seven-year-olds has left adults befuddled.
The bonus math question — which allegedly appeared on a first-grade level exam paper in Singapore — has been making the rounds on social media.
The question shows a circular puzzle with five numbers in it. There are four corresponding blanks that are meant to be filled in, but no further information is given on how to solve it.
Adults have been unable to solve it.
"Now that I can't solve this, I feel super uncomfortable," said user Kenny Eng on Facebook.
"Maybe Sheldon from the Big Bang Theory could have done this when he was seven," said Facebook user Mingli Lin.
"I just finished my course on advanced applied math and I can't solve this. Whoever set this is sick," said user Jacky Wu.
Where did the math question originally come from?
The question first surfaced on an online forum, posted by a user who claims that it was a bonus question taken from a Primary One, or first grade, examination paper.
But Singapore's Ministry of Education (MOE) couldn't confirm this. "From the image, we are unable to ascertain if the question was from a school's Primary 1 examination paper," an MOE spokesperson told Mashable in a statement.
However, the question bears a striking resemblance to one that has previously appeared on a math blog by Gordon Burgin, who calls himself an author of Maths Puzzles. (Mashable has reached out to Burgin for comment).
The two questions are almost identical, with only one difference. The bottom-left number in Mr Burgin's puzzle is 20 instead of 2.
Image: George Burgin
According to Burgin, the way to solve his puzzle is this:
Image: George Burgin
It's not the first time an exam question has left people stumped
In 2015, people in Singapore were similarly unable to solve a math question nicknamed "Cheryl's birthday."
The question was first reported to be a fifth-grade level question, but was late revealed to be a ninth-grade Maths Olympiad question.
So what is the answer to the original math question you ask?
Your guess is as good as mine.