Mental Floss

Prepare to Be Stumped By This Math Problem Meant for Fifth Graders

Alvin Ward
Good luck!
Good luck! / KARRASTOCK/Moment/Getty Images (man in horse mask); ahmad agung wijayanto/Shutterstock (question marks)

Math is hard. Just ask Mumsnet user PeerieBreeks, who once posted a “simple“ math riddle meant for fifth graders to the parenting website, and ended up with hundreds of comments—many of them from adults struggling to come up with the correct answer. Here’s the riddle:

A man buys a horse for $60. He sells the horse for $70. He then buys the horse back for $80. And he sells the horse again for $90. In the end, how much money did the man make or lose? Or did he break even?

For the most part, the problem-solvers who shared their answers all believed the man made a profit, but whether it was $10, $20, or $30 seemed to be in hot dispute. Can you figure it out? (Scroll down for the answer. We’ll give you a minute … )

the word 'answer' in a blue text bubble
Justin Dodd/Mental Floss

The wording of the riddle, not the math, seems to be what’s throwing most people off. Because the transactions in question relate to the same horse, people are looking at it as a single, four-part transaction—buys, sells, buys, sells.

But the correct way to look at the problem, and figure out the answer, is to look at it as just two transactions: A man bought a horse and sold a horse. A man bought a horse and sold a horse. (The man could just as easily have bought and sold a dog in one of those transactions and it wouldn’t change the outcome.)

All of which is to say that the correct answer is: The man made a $20 profit.

This story originally ran in 2018; it has been updated for 2022.