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written by Sam Greenspan

Math magic! Useful tricks, bar bet tricks and super random stuff with literally no practical application.

Look. We all know math tricks aren’t super badass. You don’t sit around with your friends comparing math tricks. (And if you do sit around with your friends comparing math tricks, you guys are probably far more advanced than the math tricks in this list. RDRR forever, fellas.)

But this website is a private experience. It’s just you, me and whatever software your company put on your computer to spy on you. So if you want to test these out… punch a few numbers into a calculator… jot a few things down on a piece of paper… or simply look up and off to the side as you deeply concentrate on mental math — it’ll be our secret. It’s just between you, me and the keylogger. And possibly the window washer behind you. And the guy who’s walking around from desk to desk right now saying “Mondays, huh?”

1 | The Trick Of The 11s

Since this is 11 Points and all, I felt like I should orient the first trick around the number 11. (I know some sensitive types might object to using the word “orient” in a math list, and for that I apologize.)

This is a simple multiplication trick that will allow you to multiply by 11 at will. And it’s not “multiply the number by 10 and then add it to that result.” Even though that works too. But that’s a cop out. That’s like losing weight through diet and exercise and not by doing a crazy diet like the one where you take pregnancy hormones and eat 500 calories a day.

When multiplying a two digit number by 11, the result is always first digit of the number, sum of the two numbers, last digit. Example: 11 x 18 is 198. 11 x 32 is 352. If the sum of the digits comes out greater than nine, add one to the first digit. 11 x 78 is 858.

So if someone said “What website is 64 times better than 11 Points?” you’d know it’s the website 704 Points without even busting out a calculator. (Also, if anyone does want to start a website featuring 704-item lists, I’d strongly recommend against it. Trying to get to 11 is enough to make a grown man cry.)

2 | At What Age Should You Get Married?

I like this one. It uses Euler’s number (e, which roughly equals 2.71828) to tell you the age where you have the highest probability of getting married to the ideal person.

(1) Figure out the age range when you consider yourself marriage eligible. If you’re already well into it, let’s say 22 to 45. (If you’re in Wisconsin or Minnesota, go ahead and switch that down to 18 to 24. If you’re in a major city, feel free to pump it up to 31 to 86.)

(2) Subtract the oldest age from the youngest age to calculate your total number of marryin’ years.

(3) Divide that number by e, or 2.71828.

(4) Add the result to your youngest marrying age.

So if you’ve set a range of 22 to 45, that’s 23 years. Divided by Eular’s number is 8.46. Added to 22 is 30.46, meaning that between 30 and 31 is the time when you’re at your statistical peak (and ready to stop messing around with data points and settle down with that one special data point).

3 | 111 Birthdays Of Joy

This is a trick I may or may not have been turned on to while watching the TMZ TV show. (I have a girlfriend. To those single guys out there who wonder what it’s like to have a girlfriend, the 11-word summary is “watching terrible TV, some of which you begrudgingly grow to like.”)

Now, on to the trick…

(1) Take the last two digits of the year you were born.

(2) Add that to the age you’re going to turn (or you’ve already turned) here in 2011.

The result should be… 111. Unless you were born before 1900 or after 1999. In either case, you shouldn’t be reading this website. You should be telling your life story to a biographer or putting down the piece of cake to go play outside, respectively.

4 | Deal… Or No Deal

I’m not sure if Deal Or No Deal will ever be back on TV. After all, it made Wheel Of Fortune look like a Mensa exam. I did not begrudgingly grow to enjoy watching it. But if it does come back — or if you still play the video game versions or arcade version to win prize tickets or something — here’s the quick and dirty math.

You should never take the banker’s offer unless it’s greater than the simple mean of the remaining briefcases. So if the cases you have left are $5, $50, $250, $10,000, and $400,000, you should only take an offer that’s more than $82,061. Yes, even though only one of the five cases in play has that amount.

Forget risk, forget going home empty handed, forget it. Take your brain and risk tolerance out of it and put your faith in math. That way you have something to blame. And if it screws you, just breathe a bunch of germs onto Howie Mandel.

5 | The 1001 Cloning Machine

I tried to give all the fairly sterile math tricks on this list ornate and alluring names. I think I had to work the hardest for this one. Because this is… something.

(1) Take any three digit number.

(2) Multiply it by 1,001.

The result is always the same: A six-digit number that’s your original number, twice in a row. 456 x 1001 is 456,456. And once you get a few answers and prove to yourself that this is true, jump up, point at the sky, and yell “Scheherazade!” Don’t worry. Everyone will know what you’re talking about.

6 | The Nine Folding Procedure

If you read this site, and specifically a math list on this site, you know the product of nine times any single digit number without having to think about it. So teach this trick to someone who doesn’t.

To figure out the result, hold up your hands, then fold down the finger that corresponds to the number you’re multiplying by nine. So if it’s 9 x 6, hold down your sixth finger (aka the thumb on your right hand). Then take a look at what you’ve got. Five fingers before the fold, four fingers after… the product is 54.

I remember learning this in early elementary school, then forgetting it, then remembering it again yesterday when I was researching this list. That’s quite the 25-year layoff. There’s a montage playing in my head of all the things that happened in the time between when I learned the nine folding procedure and when I remembered it. “Mr. Gorbachev, tear down this wall!” “I’m so excited, I’m so scared!” “I did not have sexual relations with that woman.” “A white Ford Bronco” and so on. All the way up to “Hide ya kids, hide ya wife.”

7 | Imaginary Taxonomy

This is a multi-step trick, so let’s all do it together…

(1) Think of a number one through 10.

(2) Multiply it by nine. Feel free to fold down your fingers if the pressure’s getting to you.

(3) Add the digits together.

(4) Subtract five from that sum.

(5) Find the letter of the alphabet that corresponds to that number (A=1, B=2, C=3, D=4, etc.)

(6) Think of a country that starts with that letter.

(7) Think of an animal that starts with the last letter of your country.

(8) Think of a color that starts with the last letter of your animal.

According to The Internet, this is where I’m supposed to tell you “Come on, man, there aren’t any orange kangaroos in Denmark!”

The only problem is that esoteric smart asses like you and me are probably thinking of amber iguanas from Djibouti or white cows from the Dominican Republic.

So I think I have to structure this joke better. Instead of subtracting five from the sum there in step four, let’s add eight. Now we should all agree on teal, tan or taupe rabbits from Qatar.

8 | Kaprekar’s Constantly Saying The Same Damn Thing

D.R. Kaprekar was an Indian mathematician. (And, coincidentally, with a January 17th birthday, Kaprekar was a Capricorn.) And while other mathematicians focused on numbers like pi or e, Kaprekar set his sights on… 6,174.

(1) Take any four digit number. (Only rule is that it has to contain at least two different numbers, so 5555 would be out, but 5554 would be OK.)

(2) Put the digits in descending and ascending order. (So if the number you picked was 7048, you’d have 8740 and 0478.)

(3) Subtract the smaller number from the larger number.

(4) If your result isn’t 6174, repeat steps two and three with your new number.

Within seven tries, you’ll end up with Kaprekar’s constant. That’s right. It’s magic. Mathemagician magic, not wingardium leviosa magic, but still magic.

9 | The Percentage Fun House Mirror

This one is useful… I don’t know, somewhere. It’s just a good trick if you every find yourself in You Got Served-style battle where instead of dancing you’re battling via calculating percentages.

And it is: x% of y = y% of x. In other words, 20 percent of 40 is the same as 40 percent of 20. Let’s see you multiply, sucka, you got nothing on me.

10 | No Way, We Have The Same Birthday, That’s So Crazy!

If there are 367 people in a room, there’s a guarantee that at least two of them will have the same birthday. (And you even account for freakish Leap Day babies.) That’s called the Pigeon Hole Principle, which says if you shove n pigeons into n-1 holes, at least one hole is guaranteed to have multiple pigeons. I have no idea why the math community is going around shoving pigeons into holes, but I have suspicions it’s connected to their inability to hold their liquor.

Also, that definitely feels like one of the analogies Charlie would’ve used on the show Numbers (err… Numb3rs) to explain to the FBI something about murderers or terrorists or something.

Now here’s the birthday twist. It’s really not that hard to get two people with the same birthday into the same room. If there are only 23 people in the room, there’s greater than a 50-50 chance that two of them will have the same birthday. And if there are 41 people in the room, it goes to a 90 percent chance.

11 | Anti-Lychrel Palindrome Syndrome (aka A Racecar Named Desire)

Through addition and inversion, you can eventually get almost any number to whittle down to a palindrome. (That is, the same forwards and backwards.) Most of them get there in seven steps or less.

Take a number down, flip it, and reverse it. (Missy Elliott style, you see.) Then add your original number and its mirror image. Repeat until you have a palindrome. Check this out…

1492 + 2941 = 4433
4433 + 3344 = 7777
525600 + 6525 = 532125
532125 + 521235 = 1053360
1053360 + 633501 = 1686861

But there are some numbers that just won’t go palindrome. Those are called Lychrel numbers. The smallest is 196. (Others include 295, 394, 493, 592, 689, 691, 788, 790, 879, 887, 978, 986, 1947 and 1997.) So don’t waste your time with them. Or you’ll be adding and inverting all day. Which is too Sisyphean, even as a time waster in class or at work.