A maths puzzle aimed at Year 2 students has adults across the internet stumped.
Shared to Twitter by UK mum Louise Bloxham, the question reads: "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 on the train to begin with?"
Not alone in her bewilderment, Bloxham's followers were also confused as to what the correct answer could be.
One method, offered by Robyn Duckworth, was to subtract 19 from 65 and add 17 to get 63.
But others insisted the answer was 65, based on the algebra working: "X - 19+17 = 63. X = 65."
The equation was also put forward by Lewis Hadlow, who concluded that it was "quite hard for a Year 2."
Bloxham further confused the debate by adding that someone had shared an answer of 46 on a Facebook forum for teachers.
"You ignore the 19 - they are a red herring presumably. So 63 - 17 = 46", they wrote.
The correct answer is in fact 65. By subtracting the 17 people who had just boarded the train from the current number of passengers, 63, you are left with 46.
You then add the first lot of 19 passengers who exited the train, reaching an answer of 65.