Learn one weird trick to solve this problem! Thanks to Nestor Abad for alerting me of a typo in an earlier version of the video. Reference https://socratic.org/questions/if-x-sqrt-x-2-1-y-sqrt-y-2-1-1-what-is-x-y Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like many YouTubers I use popular software to prepare my

# Math

The flaw which allowed the Allies to break the Nazi Enigma code. More links & stuff in full description below ↓↓↓ First video explaining Enigma: http://youtu.be/G2_Q9FoD-oQ Extra footage: http://youtu.be/BdrrJ7qd4HA Brown papers on ebay: http://bit.ly/brownpapers Periodic Videos: http://www.youtube.com/periodicvideos This video features Dr James Grime discussing Enigma, the Bombe and Alan Turing. James’ “day job” is touring

Learn the trick to this challenging algebra problem. Thanks to Ritwick in India for suggesting this problem! It comes from an IIT JEE sample paper (the JEE tests are used for admission into India’s prestigious IIT colleges). Reference https://socratic.org/questions/how-do-you-solve-6-x-4-x-9-x Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t

The Nazi’s Enigma Machine – and the mathematics behind it – was a crucial part of World War II. Flaw video at: http://www.youtube.com/watch?v=V4V2bpZlqx8 More links & stuff in full description below ↓↓↓ Brown papers on ebay: bit.ly/brownpapers Dr James Grime demonstrates the machine and discusses its many configurations. James’ “day job” is touring with the

Here’s how you do cube roots in your head! Avoid looking like Education Secretary Nicky Morgan who was stumped when asked to do a cube root: https://www.youtube.com/watch?v=x8CV0dfQMdU Note: the starting number needs to be a perfect cube. So it’s more of a magic trick: ask someone to cube a number and then you can deduce

Matt Parker reveals his pride and joy – the mysterious Parker Square! More links & stuff in full description below ↓↓↓ T-Shirt: http://bit.ly/ParkerSquareTshirt Mug and Button: https://store.dftba.com/collections/numberphile For all your Parker Square needs: http://theparkersquare.com Parker Square on Twitter: https://twitter.com/theparkersquare More magic square videos: http://bit.ly/MagicSquareVideos Matt Parker: https://www.youtube.com/standupmaths Audrey (Brady’s chihuahua): https://youtu.be/s84dBopsIe4 Support us on Patreon:

Can you solve this geometry puzzle? Thanks to Robson for the suggestion! Polish translation credit: Tłumaczenie: Przemyslav Znajdź mnie tutaj: https://forum.cdaction.pl/blogs/blog/64401-ma%C5%82a-wie%C5%9B-po%C5%9Brodku-niczego/ Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like many YouTubers I use popular software to prepare my videos. You can search for animation

French numbers can pose problems for non-native speaker – especially when you move beyond 70. Also discussing problems with phone numbers and commas! More links & stuff in full description below ↓↓↓ Featuring Dr Paul Smith from the University of Nottingham. The French and marks out of 20: http://www.youtube.com/watch?v=QzrRkhU248A A little extra unlisted bit from

This is a delightful problem. Find the area of the triangle defined by the four squares. It seems impossible but it can be solved with the right perspective. Can you figure it out? Sources Puzzle by Catriona Shearer The area of the bottom left square is 5. What’s the area of the blue triangle? pic.twitter.com/nBR32b760x

Everyone’s details below in full description. Please leave a comment about YOUR favourite number!!! More links & stuff in full description below ↓↓↓ Thanks YouTube EDU people. This video featured in order: Brady Haran (who makes Numberphile): http://www.bradyharan.com/ Derek Muller chose i – http://www.youtube.com/1veritasium Hank Green chose 2 – http://www.youtube.com/scishow Steve Spangler chose 13 –

Google asked this problem as an interview question. If the probability of seeing a car on the highway in 30 minutes is 0.95, what is the probability of seeing a car on the highway in 10 minutes? (assume a constant default probability) The video presents a solution. Blog post: http://wp.me/p6aMk-4Qk Sources http://www.impactinterview.com/2009/10/140-google-interview-questions/ http://www.businessinsider.com/answers-to-15-more-google-interview-questions-that-will-make-you-feel-stupid-2010-11#if-the-probability-of-observing-a-car-in-30-minutes-on-a-highway-is-095-what-is-the-probability-of-observing-a-car-in-10-minutes-assuming-constant-default-probability-2 If you

Squarespace: http://www.squarespace.com/numberphile More links & stuff in full description below ↓↓↓ More linguistics on Numberphile: http://youtu.be/SbZCECvoaTA Billion and Trillion: http://youtu.be/C-52AI_ojyQ Tom Scott on numbers and linguistics – a discussion with spans counties, countries, continents and the far reaches of space. Tom’s own channel is: https://www.youtube.com/user/enyay Art and animation by Pete McPartlan http://www.petemcpartlan.co.uk Support us on

What is 7×8? This video teaches how you can use your hands to multiply two numbers between 6 and 10 using your fingers. Here’s the reason the method works: https://www.youtube.com/watch?v=eEao6-F7fz8 If you like my videos, you can support me at Patreon: https://www.patreon.com/mindyourdecisions Connect on social media. I update each site when I have a new

Matt Parker discusses Tupper’s Self-Referential Formula. More links & stuff in full description below ↓↓↓ Matt’s book on Amazon (US): http://bit.ly/Matt_4D_US Matt’s book on Amazon (UK): http://bit.ly/Matt_4D_UK A little bit of extra footage from this video: http://youtu.be/wx22jdwn5zQ Thanks to our Patreon supporters… Herschal Sanders (from Susan) Today I Found Out Christian Cooper Ken Baron Greg

Many students in the UK had difficulty with a similar problem on the GCSE exam. What’s the rectangle’s area, given the three circles are identical with radius r? Watch the video to learn how to solve this problem. Sources Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Playlist to watch all videos on MindYourDecisions: https://www.youtube.com/playlist?list=UUHnj59g7jezwTy5GeL8EA_g Send me your favorite puzzles/suggestions by

A game to play on the elliptical table: http://youtu.be/3WHBlPvK3Ek More links & stuff in full description below ↓↓↓ And more extra footage: http://youtu.be/pulp55gTKGE Alex Bellos’ Loop Table website: http://www.loop-the-game.com Alex discusses the topic in his book Alex Through the Looking-Glass (UK) and The Grapes of Math (US)… http://bit.ly/BellosBooks Support us on Patreon: http://www.patreon.com/numberphile NUMBERPHILE Website:

In a square, a line is drawn from the bottom left corner with length 12 to the interior of the square. From the end of that line, a perpendicular is drawn going up and left with length 3. From the end of that line, another perpendicular is drawn going up and right with length 9.

Our Pi Playlist (more videos): http://bit.ly/PiPlaylist Steve Mould (tau) and Matt Parker (pi) go head-to-head. More links & stuff in full description below ↓↓↓ See our tau video: http://www.youtube.com/watch?v=83ofi_L6eAo And check our Pi videos: http://www.youtube.com/playlist?list=PL4870492ACBDC2E7C Matt Parker: http://www.standupmaths.com/ Steve Mould: http://www.stevemould.com/ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by

You can multiply two numbers if you know how to double, halve, and add up numbers. This is really interesting: basically the Egyptians were using binary multiplication! Watch the video to see how it works. READ why this method works: http://mindyourdecisions.com/blog/2014/08/27/the-egyptian-method-russian-peasant-multiplication-video-and-a-proof/#.U_5I5vldV8E WATCH how ancient Egyptians divided numbers: https://www.youtube.com/watch?v=bKqQGISplMo This method is documented in the Rind

See our other Graham’s Number videos: http://bit.ly/G_Number A number so epic it will collapse your brain into a black hole! Yet Tony Padilla and Matt Parker take the risk of discussing its magnitude. Watch with caution. More links & stuff in full description below ↓↓↓ See also our video about the Googol and Googolplex at:

A gigantic pie is shared with 100 guests, and each guest gets an increasing percentage of the remaining pie. Who gets the largest piece? Sources https://www.theguardian.com/science/2017/jun/19/did-you-solve-it-pythagorass-best-puzzles https://puzzling.stackexchange.com/questions/52787/who-get-the-biggest-piece Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Playlist to watch all videos on MindYourDecisions: https://www.youtube.com/playlist?list=UUHnj59g7jezwTy5GeL8EA_g This is the only channel to feature math topics suggested by people around the world. Support on Patreon

Prime numbers, Ulam Spirals and other cool numbery stuff with Dr James Grime. More links & stuff in full description below ↓↓↓ James Clewett on spirals at: http://youtu.be/3K-12i0jclM And more to come soon… * subscribing to numberphile does not really change your physical appearance! And “golden line” in this context was made up by Brady!

The 1947 Stanford Competitive Examination included a version of this problem. Reference https://www.cut-the-knot.org/Outline/Arithmetic/DivisionBy72.shtml Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like many YouTubers I use popular software to prepare my videos. You can search for animation software tutorials on YouTube to learn how to

0! = 1 Dr James Grime tries to explain why this is the case – follow James on Twitter at https://twitter.com/jamesgrime More links & stuff in full description below ↓↓↓ Regarding the equation at the end – James says it should be e^-t dt NOT e^-n dn … sorry for the mix-up! NUMBERPHILE Website: http://www.numberphile.com/

The internet is loving this math trick which makes many calculations much easier! Sources/references Fascinating little life hack, for doing percentages: x% of y = y% of x So, for example, if you needed to work out 4% of 75 in your head, just flip it and and do 75% of 4, which is easier.

Main video is at: http://youtu.be/seUU2bZtfgM This is some extra stuff from Simon Pampena we didn’t use in the first video! More links & stuff in full description below ↓↓↓ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by Brady Haran Patreon: http://www.patreon.com/numberphile Brady’s videos subreddit: http://www.reddit.com/r/BradyHaran/ Brady’s latest videos across

This simple problem for kids is sure to stump some adults. Can you figure out the height of the table? Problem adapted from #quiz Here is a math word problem from a Chinese elementary school student's homework. Have a try to figure it out! Leave your answer in the comment. pic.twitter.com/kOlydqNDQO — China Focus (@China__Focus)

Featuring Ben Sparks discussing the Mandelbrot Set (and Julia Sets). Catch a more in-depth interview with Ben on our Numberphile Podcast: https://youtu.be/-tGni9ObJWk More links & stuff in full description below ↓↓↓ More videos with Ben: http://bit.ly/Sparks_Playlist Ben Sparks website: https://www.bensparks.co.uk And on Twitter: https://twitter.com/sparksmaths Holly Krieger has done a few Mandelbrot videos on Numberphile… The

On the JEE Advanced test, you would only have minutes to solve this problem. Students preparing for the exam often take coaching to prepare. In this video I want to focus on the mathematical content of this beautiful problem. A special thanks this month to The Laba Family, Michael Anvari, Richard Ohnemus, Shrihari Puranik, Kyle.

We mark the date 12/12/12 with a video about the merits of the dozenal/duodecimal system. More links & stuff in full description below ↓↓↓ Numberphile regular Dr James Grime makes the case. More about James at http://www.singingbanana.com/ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by Brady Haran Patreon: http://www.patreon.com/numberphile

This is a fun little geometry problem. Source Bilal Sarımeşeli tweet #math #geometry #teachertwitter #questiontime Find the radius of the circle. pic.twitter.com/C1l5P2iAvN — Bilal Sarımeşeli (@bilalsarimeseli) September 26, 2019 Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like many YouTubers I use popular software to

We’re talking pretty big numbers here… And an interesting idea about what it’d be like traveling in a Googolplex-sized Universe! More links & stuff in full description below ↓↓↓ With Antonio (Tony) Padilla and Ria Symonds from the University of Nottingham. About the brown paper: http://periodicvideos.blogspot.com/2012/02/brown-paper-question.html NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets:

What fraction of the entire circle is shaded? Special thanks this month to: Michael Anvari, Kyle, Mike Robertson. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Jobbings, A. (2011). The Mathematical Gazette https://www.cambridge.org/core/journals/mathematical-gazette/article/9564-two-semicircles-fill-half-a-circle/6365F0D492DF2E682E71A891C782CAF6 The chalice problem Azimuth Project (John Carlos Baez) Geometry Puzzles Folding proof by Greg Egan http://math.ucr.edu/home/baez/mathematical/semicircle_puzzle_egan.gif Cut The Knot https://www.cut-the-knot.org/proofs/Semicircles.shtml Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send

The knight’s tour and magic knight’s tour. More links & stuff in full description below ↓↓↓ The first magic tour has an error (my fault in animation) with 62 and 64 transposed…. See here: http://periodicvideos.blogspot.co.uk/2014/01/oops.html Brown papers: http://bit.ly/brownpapers Some good knight’s tour links: Great overview by Ben Hill and Kevin Tostado: http://bit.ly/1hYHoLE Notes and huge

You have a full 12 liter jug and empty 5 and 8 liter jugs. Can you measure exactly 6 liters? This problem dates to 1484 and was posed in the context of a milkman making a home delivery to a customer. The story goes this riddle so delighted Simeon Denis Poisson as a young boy

Featuring Tadashi Tokieda – more Tadashi videos at: http://bit.ly/tadashi_vids More links & stuff in full description below ↓↓↓ Tadashi Tokieda is a Professor of Mathematics at Stanford University (though this was filmed when he was at Cambridge, in the UK). Animation by Pete McPartlan. Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile

It may not be exactly 99 percent, but many people will get the incorrect answer. It’s a great teaching opportunity. Learn how to solve this problem! (There are multiple ways, I am presenting one valid method). Previous video Source https://www.instagram.com/p/BxOfZBVB2Mo/ Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though

Famously beautiful, the Mandelbrot Set is all about complex numbers. Featuring Dr Holly Krieger from MIT. More links & stuff in full description below ↓↓↓ The next part is on Numberphile2 at: http://youtu.be/oCkQ7WK7vuY Animation courtesy of team fresh. Check out more at: http://hd-fractals.com — Music: Alan Stewart. Support him at http://bit.ly/1sdwTHF More videos with Holly