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Garth SundemRSS Feed of this column.

Garth Sundem is a Science, Math and general Geek Culture writer, TED speaker, and author of books including Brain Trust: 93 Top Scientists Dish the Lab-Tested Secrets of Surfing, Dating, Dieting... Read More »

Even though you're already the mathematical Wizard of Oz, you can still benefit from the Wow factor of hoisting a new curtain of number tricks to impress your friends and intimidate your enemies.

Here, dear geek, are three nifty mind widgets to make mates want you and peers want to be you.

Multiply up to 20x20
1. For example, take 17x13
2. Place the larger number on top, in your head
3. Imagine a box, encompassing the 17 and the 3
4. Add these to make 20
5. Add a zero to this, to make it 200
6. Multiply the 7 and the 3 to get 21
7. Add this to 200 to get the answer: 221

Multiply any two-digit number by 11
1. For example, take 79
House of Straw
Use six straws to create the classic house shape (a rectangular body with two straws forming the roof, all laying flat on the table). Bet that you can make four equal triangles by moving only three straws. Try it! To all but the most creatively freethinking, this is impossible. The trick is to go 3D—pick up the three straws that make the bottom and sides of the rectangle and replace them so that one end of each straw is rooted in a corner of the triangle with all three moved straws touching above the center of the original triangle, like a tent or teepee—four, equal triangles, each the size of the original roof.

Paper Match
True Math Genius
This trick will bring a smile to the face of even the most hardened math geek. First, lay matches on a table to form the equation I + II + III = IIII (crossed matches make the plus signs and parallel matches make the equals sign). Challenge your opponent to make this statement true by moving only one match and without messing with the sum after the equals sign. The trick is to pick up one match from the II, and lay it across the middle match in the III, making the full equation read:
I + I + I + I =IIII.

Two Glasses II
Newton’s apple fell from the tree and after thumping the scientist on the head, fell benignly to the ground. If the same apple fell toward Einstein (and happened to have a little added atomic oomph), it could, according to special relativity, become infinitely massive, flattening not only the unfortunate Einstein as he sat bodhisattva-like beneath the tree, but also the Earth itself.

This doesn’t mean Newton was wrong—only, that his theories apply more accurately to things traveling at speeds that don’t approach the speed of light (from slow-moving atomic particles to city transit busses). The crucial postulate of Einstein’s theory is the idea that the speed of light is measured to be exactly the same no matter the motion of the observer.
Do you have what it takes to be Scientific Blogging's alpha geek? Well it’s time put your geek where your mouth is…IF YOU CAN!

But first a warning: yes, you could Google for these answers, but then, deep down, you’ll know you’re a bad person. Then again, you might win a free Geeks’ Guide to World Domination. So you’ll have to balance total loss of self worth with free geek schwag. It’s up to you.
D'you dig the Geek Off? Did you email your answers to If not, too late sucka! That is, too late until Monday morning, when we play another round of the feud. Yep, every week there's a Geek Off and every week you can win a free Geeks' Guide to World Domination: Be Afraid, Beautiful People. Check the quiz Monday, email your answers 'til Friday at midnight EST, then check the answers and fight about corrections starting Saturday

Here are the answers to last week's geek off:
1. Geek Culture/Ephemera
Blackbeard: 4, C, d
Black Bart: 2, B, b
Mary Read: 4, D, a
Jean Lafitte: 1, A, c