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

iStock
iStock

Math is hard. Just ask Mumsnet user PeerieBreeks, who posted a ‘simple’ math riddle meant for fifth graders to the parenting website, and ended up with more than 500 comments—many of them from adults struggling to come up with the correct answer. Here’s the riddle:


For the most part, the problem-solvers who shared their answers all believed that 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 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.

13 Father's Day Gifts for Geeky Dads

Amazon/Otterbox/Toynk
Amazon/Otterbox/Toynk

When in doubt, you play the hits. Watches, flasks, and ties are all tried-and-true Father’s Day gifts—useful items bought en masse every June as the paternal holiday draws near. Here’s a list of goodies that put a geeky spin on those can’t-fail gifts. We’re talking Zelda flasks, wizard-shaped party mugs, and a timepiece inspired by BBC’s greatest sci-fi series, Doctor Who. Light the “dad” signal ‘cause it’s about to get nerdy!

1. Lord of the Rings Geeki Tikis (Set of Three); $76

'Lord of The Rings' themed tiki cups.
Toynk

If your dad’s equally crazy about outdoor shindigs and Tolkien’s Middle-earth, help him throw his own Lothlórien luau with these Tiki-style ceramic mugs shaped like icons from the Lord of the Rings saga. Gollum and Frodo’s drinkware doppelgängers each hold 14 ounces of liquid, while Gandalf the Grey’s holds 18—but a wizard never brags, right? Star Wars editions are also available.

Buy it: Toynk

2. Space Invaders Cufflinks; $9

'Space Invaders' cufflinks on Amazon
Fifty 50/Amazon

Arcade games come and arcade games go, but Space Invaders has withstood the test of time. Now Pops can bring those pixelated aliens to the boardroom—and look darn stylish doing it.

Buy it: Amazon

3. Legend of Zelda Flask; $18

A 'Legend of Zelda' flask
Toynk

Saving princesses is thirsty work. Shaped like an NES cartridge, this Zelda-themed flask boasts an 8-ounce holding capacity and comes with a reusable straw. Plus, it makes a fun little display item for gamer dads with man caves.

Buy it: Toynk

4. AT-AT Family Vacation Bag Tag; $12

An At-At baggage tag
ShopDisney

Widely considered one of the greatest movie sequels ever made, The Empire Strikes Back throws a powerful new threat at Luke Skywalker and the Rebellion: the AT-AT a.k.a. Imperial Walkers. Now your dad can mark his luggage with a personalized tag bearing the war machine’s likeness.

Buy it: ShopDisney

5. Flash Skinny Tie; $17

A skinny Flash-themed tie
Uyoung/Amazon

We’ll let you know if the Justice League starts selling new memberships, but here’s the next best thing. Available in a rainbow of super-heroic colors, this skinny necktie bears the Flash’s lightning bolt logo. Race on over to Amazon and pick one up today.

Buy it: Amazon

6. Captain America Shield Apron; $20

A Captain America themed apron
Toynk

Why let DC fans have all the fun? Daddy-o can channel his inner Steve Rogers when he flips burgers at your family’s Fourth of July BBQ. Measuring 31.5 inches long by 27.5 inches wide, this apron’s guaranteed to keep the cookout Hydra-free.

Buy it: Toynk

7. Doctor Who Vortex Manipulator LCD Leather Wristwatch; $35

A Doctor Who-themed watch
Toynk

At once classy and geeky, this digital timepiece lovingly recreates one of Doctor Who’s signature props. Unlike some of the gadgets worn on the long-running sci-fi series, it won’t require any fancy chronoplasm fuel.

Buy it: Toynk

8. Wonder Woman 3-Piece Grill Set; $21

Wonder Woman three-piece gill set
Toynk

At one point in her decades-long comic book career, this Amazon Princess found herself working at a fast food restaurant called Taco Whiz. Now grill cooks can pay tribute to the heroine with these high-quality, stainless steel utensils. The set’s comprised of wide-tipped tongs, a BBQ fork, and a spatula, with the latter boasting Wonder Woman’s insignia.

Buy it: Toynk

9. Harry Potter Toon Tumbler; $10

Glassware that's Harry Potter themed
Entertainment Earth

You can never have too many pint glasses—and this Father’s Day, dad can knock one back for the boy who lived. This piece of Potter glassware from PopFun has whimsy to spare. Now who’s up for some butterbeer?

Buy it: EntertainmentEarth

10. House Stark Men’s Wallet; $16

A Game of Thrones themed watch
Toynk

Winter’s no longer coming, but the Stark family's propensity for bold fashion choices can never die. Manufactured with both inside and outside pockets, this direwolf-inspired wallet is the perfect place to store your cards, cash, and ID.

Buy it: Toynk

11. Mr. Incredible “Incredible Dad” Mug, $15

An Incredibles themed mug
ShopDisney

Cue the brass music. Grabbing some coffee with a Pixar superhero sounds like an awesome—or dare we say, incredible?—way for your dad to start his day. Mom can join in the fun, too: Disney also sells a Mrs. Incredible version of the mug.

Buy it: ShopDisney

12. Star Wars phone cases from Otterbox; $46-$56

Star Wars phone cases from OtterBox.
Otterbox

If your dad’s looking for a phone case to show off his love of all things Star Wars, head to Otterbox. Whether he’s into the Dark Side with Darth Vader and Kylo Ren, the droids, Chewbacca, or Boba Fett, you’ll be able to find a phone case to fit his preference. The designs are available for both Samsung and Apple products, and you can check them all out here.

Buy it: Otterbox

13. 3D Puzzles; $50

3D Harry Potter puzzle from Amazon.
Wrebbit 3D

Help dad recreate some of his favorite fictional locations with these 3D puzzles from Wrebbit 3D. The real standouts are the 850-piece model of Hogwarts's Great Hall and the 910-piece version of Winterfell from Game of Thrones. If dad's tastes are more in line with public broadcasting, you could also pick him up an 890-piece Downton Abbey puzzle to bring a little upper-crust elegance to the homestead.

Buy it: Hogwarts (Amazon), Winterfell (Amazon), Downton Abbey (Amazon)

At Mental Floss, we only write about the products we love and want to share with our readers, so all products are chosen independently by our editors. Mental Floss has affiliate relationships with certain retailers and may receive a percentage of any sale made from the links on this page. Prices and availability are accurate as of the time of publication.

How to Brew Your Own Fluorescent Beer at Home

The Odin
The Odin

If you're one of the many people who made their own sourdough starter in quarantine, you already know yeast is a living thing. That means its biological makeup can be tweaked using genetic engineering. As Gizmodo reports, that's exactly what a former NASA biologist has done to create his new fluorescent yeast kits.

A few years ago, Josiah Zayner left his job as a synthetic biologist for NASA to found The Odin, a company that lets anyone experiment with genetic science at home. His recently launched yeast kit accomplishes this in an eye-catching way. Thanks to a fluorescent protein from jellyfish, yeast that's been genetically modified with the kit glows green under a black or blue light.

Despite looking like a prop from a sci-fi film, the yeast is still yeast. That means it can be used in home-brewing projects if you want to take the science experiment a step further. According to Eater, yeast made with the kit ferments and fluoresces when added to honey and water. If you brew a batch of beer with the right amount of yeast, the final product will emit an otherworldly glow when viewed under a blacklight. The kit hasn't been FDA approved, but the company states the materials are nontoxic and nonallergenic, and beer made with it will still taste like beer.

You can purchase a fluorescent yeast kit from The Odin's online shop for $169. If you're looking for more ways to experiment with genetic technology at home, the company also sells kits that let you play with frog and bacteria DNA.

[h/t Gizmodo]