## Thanks To A Mathematical Trick, You Can Always 'Guess' What Random Number A Person Has Picked

You might think it's mind reading, but really, it's just about math.

WHAT'S MY NUMBER?

You might think it's mind reading, but really, it's just about math.

IT ALL ADDS UP

It's no secret that Americans aren't exactly leading the pack in mathematics.

COUNT 'EM AND WEEP

A computer can make a decision faster. That doesn't make it fair.

FOLLOW THE NUMBERS

An interactive map of mathematics as it stands today, mathematics as it is practiced by mathematicians. From simple starting points — Numbers, Shapes, Change — the map branches out into interwoven tendrils of thought.

GALAXY BRAINS

New research has exploded the space of problems that quantum computers can efficiently verify, simultaneously knocking down milestone problems in quantum physics and math.

WE'RE ALL MATHEMATICIANS NOW

Looking for the answers to ax² + bx + c = 0? A mathematician has rediscovered a technique that the ancient Babylonians used.

WHOA

Johnny Ball explains the brilliance of the Russian method of multiplication.

BUCKLE UP...

By exploiting randomness, three mathematicians have proved an elegant law that underlies the chaotic motion of turbulent systems.

PATTERNS ARE HARD TO DETECT

Tracking the spread of disease requires precision and math. But super-spreaders, who transmit germs faster and further than other patients, can confound the model.

HUMAN ERROR

Doing so was inadvertent, but it taught me an important lesson.

CONSTANT WONDER

From dripping faucets to the population growth of rabbits, the bifurcation diagram exists and can be applied in so many places.

THREE SIDES TO THE STORY

I reached out to several geometry experts to see if we could arrive at a consensus answer. Turns out virtually all of the mathematicians I contacted found the same solution — but not all of them figured it out in the same way.

BEE SQUARED

As Scarlett Howard taught honeybees to do arithmetic, they showed her how fundamental numbers might be to all brains.

IF THERE WAS A PROBLEM, YO I'LL SOLVE IT

Computer scientists are buzzing about a new mathematical proof that proposes a quantum-entangled system sort of like the one described above. It seems to disprove a 44-year-old conjecture and details a theoretical machine capable of solving the famous halting problem, which says a computer cannot determine whether it will ever be able to solve a problem it's currently trying to solve.

GOTTA DO YOUR HOMEWORK

To escape from the room, you must enter into the keypad the correct answer to the question 230 x 10 + 2. As can be seen from this video, filmed from the perspective of the creator, it's not as easy a question as it seems.

HANGS IN THE BALANCE

In "The History of the University of Cambridge," author Edmund Carter praises the bridge as "one of the most curious pieces of carpentry of this kind in England."

TURING THE TIDE

Just four percent of the Turing Award's winners have been women. That lack of recognition has consequences.

ELECTRIC AVENUE

Jason Fenske does the math on the Porsche Taycan, the company's first full-electric sports car — and finds it likely is faster than the Tesla Model S.

GOOD + BOI = TREAT

A new study suggests dogs can quickly estimate numerical values in a similar manner to humans and other primates.

IT ALL COMES BACK TO MATH

Want to solve a Rubik's Cube? Then you have to know the numbers. Here's the amazing math behind the legendary toy, and how to use it to solve the puzzle.

MATH BLASTERS

Mathematicians regard the Collatz conjecture as a quagmire and warn each other to stay away. But now Terence Tao has made more progress than anyone in decades.

FAR OUT

We finally know how big a set of numbers can get before it has to contain a pattern known as a "polynomial progression."

5318008

These $100 calculators have been required in classrooms for more than twenty years, as students and teachers still struggle to afford them

'KIRBY SUCKS'

It was for a party where attendees come prepared with a three-minute lecture to deliver to their friends. You know, for fun.

CUT YOUR LOSSES

In today's pettiest battles, NYC lashes out against people who can't afford to take their stupid trains.

A HEAD ABOVE THE REST

It's difficult to effectively refute the claim that John von Neumann is likely the most intelligent person who has ever lived.

NEUTRINO + NEUTRINO = ?

Three physicists stumbled across an unexpected relationship between some of the most ubiquitous objects in math.

TAKE ME DOWN TO PARADOX CITY

Mathematicians have figured out exactly how many moves it takes to randomize a 15 puzzle.

WEIGHT WEIGHT DON'T TELL ME

Does a balance measure mass or weight? It's not always clear.

WHAT'S YOUR NUMBER?

Statistics shows that there is an optimal stopping time in terms of dating and finding a partner. YouTuber The Action Lab sets out to test whether that theory really works.

PLOTTING SUCCESS

She fled the Nazis, only to face a new challenge: being accepted in academia.

OW, MY BRAIN

Welcome to The Riddler, a weekly collection of problems related to math, logic and probability. Can you solve these?

YOU SAY EQUAL, I SAY EQUAL-ISH

The equal sign is the bedrock of mathematics. But there is a growing community of mathematicians who regard it as math's original error: "It should have been equivalence all along."

WON'T STAND FOR THIS

The unspoken escalator etiquette says those who stand should stay on the right so stair-walkers like me can pass on the left. Apparently this is all wrong. Walking may be faster for me, but it slows everybody else down.

NOT OK, COMPUTER

Most high school math classes are still preparing students for the Sputnik era. Here's the case for an overhaul — and a new focus on data fluency.

FAST AND PRUDENT

Here's how to strike the optimal balance of parking close to the entrance without wasting too much time circling.

TRUST, BUT REVERIFY

"I think there is a non-zero chance that some of our great castles are built on sand," he said, arguing that we must begin to rely on AI to verify proofs.

EXCUSE ME, AUNT SALLY

The way you learned to multiply works, but computers employ a faster algorithm.

HAPPY LITTLE MATH PROBLEMS

Australian Toby Hendy attempts to make mathematical problems more accessible by using the Bob Ross method.

6 STILL AFRAID OF 7

Just on the heels of finding three cubed numbers that sum to 42, scientists have passed another important milestone by finding three enormous cubes that sum to 3.

FROGGER IN REAL LIFE

Can you figure out this math problem involving a frog's approximate amount of leaps it needs to get to the other side of the river?

IRRATIONALLY SPEAKING...

Mathematicians have finally proved a conjecture on approximating numbers with fractions

N IS VERY ODD

We're one step closer to solving an 82-year-old math riddle that has stumped the world's smartest mathematicians. But a complete answer could still be far away.

GOING WITH THE FLOW

"It turns out that computers are really bad at generating random numbers. The only thing worse than generating random numbers on computers is humans generating random numbers."

WHAT ARE THE CHANCES?

Does objective, perfect randomness exist, or is randomness merely a product of our ignorance?

NO MORE 3.14159265358979323846264338327

The ancient Greeks wondered when "irrational" numbers can be approximated by fractions. By proving the longstanding Duffin-Schaeffer conjecture, two mathematicians have provided a complete answer.

DOESN'T COUNT

It's formatted to confuse people, and there are no interesting underlying concepts.

NAP, WAKE UP, NAP, WAKE UP, NAP, WAKE UP...

New parents do not get a lot of sleep.

'IT IS JUST BEAUTIFUL, LIKE A PRECIOUS PEARL'

The "sensitivity" conjecture stumped many top computer scientists, yet the new proof is so simple that one researcher summed it up in a single tweet.

AND THEY CAN SHOW YOU THE NUMBERS

Nearly everyone I have spoken to in the R community credits R-Ladies for increasing the number of women who use the language, as well as making the community more comfortable for women and other gender minorities (R-Ladies welcomes all those who don't identify as men).

RISK, REWARD AND RIDING

There are mountains of evidence suggesting cycling increases longevity, but sometimes, I can't help but hypothesize: It's safer to never ride a bike at all.

NEVER DIVIDE YOUR FRIENDS

We break down one of the most mystical energies in the universe.

FOLLOW THE FORMULA

Even though not all driver's exams require you to parallel park, sometimes real life does.

VIVE LA METRIC RESISTANCE

American units of measurement are sort of dumb, but also sort of smart.

IT DIDN'T ADD UP

In just three pages, a Russian mathematician has presented a better way to color certain types of networks than many experts thought possible.

ON A SOCIETY THAT'S 'AFRAID OF MATH'

We discussed his experiences in sports media, whether advanced statistics are making sports more efficient and less fun and racism around high-level math.

.9999 = 1?

We are flabbergasted that our math teachers deprived us of these simple yet handy tricks.

WHEN IT DOESN'T ADD UP

Our hectic, on-demand lifestyles rely upon allocating finite sets of resources to constantly changing numbers of people. As this task grows ever harder, it will require solutions to a little-known mathematical riddle.

MASS EFFECT

Attempts have been made to define the units of measurement over the years. But on Monday, International Metrology Day, there was a complete revision of those standards.

SLEIGHT OF HAND

How a renowned researcher beat the odds, stumped casino owners around the world and walked away with a fortune.