A man gives his girlfriend an excruciating lesson in maths in this viral video.
YouTube user xmintyx filmed the exchange, which took place during a bedtime chat.
Lying under the duvet, the couple argue over the correct answer to an ages-old riddle: "A big brother is four years old. A little brother is half his age. How old will the little brother be when the big brother is 100?"
Before you answer, see if you fall into the same logic trap as the girlfriend.
She is entirely convinced that given the little brother is "half the age" of the big brother, the answer must be 50.
Read more:
"How is it not 50?" she pleads with her boyfriend, after he repeatedly tells her it's the wrong answer.
"You said the little brother is half the big brother's age," she reasons.
"So when the big brother is 100 he's going to be half 100 which is 50!".
Like all riddles, the trick is in the wording of the question.
By focusing on the fact that the brother is "half the age" of his sibling, she fails to pick up on the fact that he in in fact simply two years younger.
So when the boyfriend explains that the younger brother will in fact be 98 when the big brother is 100, it takes a while for the penny to drop.
"I think you've got this wrong," she says, before finally laughing: "Oh I get it!"
