Can you solve this tricky question from the CSAT? Thanks to Sean from South Korea for the suggestion! Special thanks this month to: Mike Robertson, Michael Anvari, Kyle. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I cannot reply to everyone but I consider all ideas! […]

# Category Archives: Math

## What is the area? A nice problem from Singapore

Can you solve this challenging problem from the Mathematical Olympiad of Singapore? Thanks to Truong from Vietnam for the suggestion! Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I cannot reply to everyone but I consider all ideas! Like many YouTubers I use popular software to prepare my videos. You can search for […]

## A Simple Puzzle Stumps Many Adults. Can You Solve It?

“You have to solve this yourself, otherwise you won’t see how beautiful it is,” Lee Sallows. SoraNews24 Sinisterly simple math puzzle for elementary school kids stumps Japanese Twitter adults IT Media (Japanese) https://nlab.itmedia.co.jp/nl/articles/1706/15/news078.html Nob’s Number Puzzle (Nobuyuki Yoshigahara (芦ヶ原 伸之)) https://dodona.ugent.be/en/exercises/1191761379/ Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I cannot reply to […]

## Gabriel’s Horn Paradox – Numberphile

Featuring Tom Crawford. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ Extra footage from this interview: https://youtu.be/EsX9y0lKsZw Tom Crawford’s website, with links to his work and other outreach: https://tomrocksmaths.com More Tom Crawford videos on Numberphile: http://bit.ly/Crawford_Videos Infinity Paradoxes: https://youtu.be/dDl7g_2x74Q Vuvuzelas on Sixty Symbols […]

## A lovely riddle

Can you solve this challenging Valentine’s Day problem? Thanks to Stéphane from Belgium for the suggestion! Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address at end of many videos). I may not reply but I do consider all ideas! If you buy from the links below I may receive a commission for sales. (As an […]

## A Radical Sum

This was asked to students in Indonesia. Can you figure it out? Special thanks this month to: Michael Anvari, Kyle, Mike Robertson. Thanks to all supporters on Patreon! Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I cannot reply to everyone but I consider all ideas! Like many YouTubers I use popular software […]

## A Curious Fact About Semicircles!

What fraction of the entire circle is shaded? 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 me suggestions by email (address in video). I cannot reply to everyone but I consider all ideas! […]

## Annoying Puzzles (and Cognitive Reflection Problems) – Numberphile

This video features Tim Harford. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ See an extra snippet from this interview on Numberphile2: https://youtu.be/1lwocqnBmVc Tim Harford website: https://timharford.com How to Make the World Add Up: https://amzn.to/3oBcDRx Or (different title in the US): The Data […]

## What is the sum? The answer is “too” good!

Can you solve this challenging algebra problem? Source https://math.stackexchange.com/questions/3844738/if-x5-1-with-x-neq-1-then-find-value-of-fracx1x2-fracx21x4 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 make videos. Be prepared–animation […]

## A proof that e is irrational – Numberphile

Professor Ed Copeland shows a proof by Joseph “Voldemort” Fourier that e is irrational. Check out episode sponsor http://KiwiCo.com/Numberphile for 50% off your first month of any subscription. The crates are great! More links & stuff in full description below ↓↓↓ Ed Copeland is a physics professor at the University of Nottingham. Check out more […]

## What Is The Square’s Area?

Can you solve this delightful problem? Thanks to Elmer for the suggestion! Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I cannot reply to everyone but I consider all ideas! Like many YouTubers I use popular software to prepare my videos. You can search for animation software tutorials on YouTube to learn how […]

## Quasiperfect Numbers with Eric Lander – Numberphile

Eric Lander discusses how quasiperfect numbers gave him a start… More links & stuff in full description below ↓↓↓ This interview was filmed in 2015 but remained unedited and unpublished until now… The other main interview from that day (about “Basic Research”) can be found here: https://youtu.be/6gnsQjPCC78 The Westinghouse Science Talent Search has since become […]

## WOW! A very satisfying answer

Thanks to Hrigved for the suggestion! 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 make videos. Be prepared–animation is time consuming […]

## Triangles In A Row

Can you solve for the shaded area? 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 make videos. Be prepared–animation is time […]

## The Drag Equation (Empire State Building v Eiffel Tower) – Numberphile

Tom Crawford discusses drag – then we drop the Empire State Building and Eiffel Tower into the ocean… Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ Find out more about Tom Crawford: https://tomrocksmaths.com/about/ More Tom videos on Numberphile: http://bit.ly/Crawford_Videos Check out some raw […]

## Simple puzzle everyone is talking about #Shorts

They say “You should be able to solve this,” but the internet can’t agree on the answer! What do you think? #Shorts MindYourDecisions poll results https://www.youtube.com/post/Ugzv_XryKGRUCCNDluN4AaABCQ The Moscow Puzzles (problem 37) by Boris A. Kordemsky, edited by Martin Gardner http://www.math.cmu.edu/~bkell/21110-2010s/algebra-puzzles.pdf https://www.doverpublications.com/mathsci/0718/d/270785_Easy_Answers.pdf Related memes https://www.physicsforums.com/threads/math-puzzle.477209/ https://knowyourmeme.com/forums/just-for-fun/topics/14038-you-really-should-be-able-to-solve-this Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 If you buy from the links below I […]

## Incredible Puzzle – Quadrilateral Around A Semicircle

A quadrilateral wraps around a semicircle. The two flanking sides are equal to 9 and 16, and the semicircle is centered along the base side. Can you solve for the length of the base side? It’s a challenging and fun problem! Special thanks this month to: Mike Robertson, Michael Anvari, Kyle. Thanks to all supporters […]

## Solving MIT’s Father Son Riddle

MIT is one of the top ranked universities in the world. Can you solve this question from their 1876 admissions test? Source https://web.archive.org/web/20190703223047/https://libraries.mit.edu/archives/exhibits/exam-entrance1876/algebra1876.html 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 […]

## 5 Rectangles Puzzle

Thanks to Surjadi from Indonesia for the suggestion! Twitter Cshearer41 A square is split into five rectangles with equal areas. What’s the area of the square? pic.twitter.com/wtuEjxMASI — Catriona Agg (@Cshearer41) July 11, 2020 solution by @birkhofyan pic.twitter.com/3EIij7DjaU — Birkan Yıldız (@birkhofyan) July 11, 2020 Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). […]

## Butterflies and Gyroids – Numberphile

Dr Sabetta Matsumoto discusses some of the mathematics of colour in nature, including butterfly wings and soap films. More links & stuff in full description below ↓↓↓ Dr Matsumoto’s group at Georgia Tech: http://matsumoto.gatech.edu And her Twitter: https://twitter.com/sabetta_ Previous video with Sabetta on Numberphile: https://youtu.be/0e5vzTsLh2s Brady looks at butterflies on Objectivity: https://youtu.be/lJWHppdupbI Numberphile is supported […]

## Can You Solve Euler’s Egg Riddle?

Thanks to Francisco from Portugal for the suggestion! They say Euler asked this tricky algebra problem to his students. Reference Euler’s Riddle 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 […]

## Inca Knot Numbers – Numberphile

Alex Bellos discusses how the Incans used knots in string (Quipu) to record numbers. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ Check out the Language Lover’s Puzzle Book) on Amazon: https://amzn.to/3oU0wjT Or a signed version from Maths Gear: https://bit.ly/Language_Lovers More Alex on […]

## Overlapping Triangles Puzzle

Can you solve this delightful problem? Sources Catriona Agg (@Cshearer41) When I place two 3-4-5 triangles like this, what’s the overlapping area? pic.twitter.com/XsTf2ic0i0 — Catriona Agg (@Cshearer41) February 16, 2019 Nèstor Abad proof 1/2 (3·4/2) = 3. pic.twitter.com/C0NC6QlDq1 — Nèstor Abad (@nabadvin) February 16, 2019 Ignacio Larrosa Cañestro animation As Nèstor said, it can be […]

## How to build a Giant Dome – Numberphile

Tom Crawford speaks about domes, curves, and catenaries. Check out http://KiwiCo.com/Numberphile for 50% off your first month of any subscription. More links & stuff in full description below ↓↓↓ Tom Crawford: https://tomrocksmaths.com/ More videos with Tom: http://bit.ly/Crawford_Videos Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, […]

## Killer Problem With A Golden Answer

Can you solve this “coffin” problem? Thanks to Rahul for the suggestion! Special thanks this month to: Kyle, Mike Robertson, Michael Anvari. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Adapted from problem 4 of Jewish Problems by Tanya Khovanova, Alexey Radul https://arxiv.org/abs/1110.1556v2 Coffin Problem ft. blackpenredpen: Cube and Cube Root (Mu Prime Math) Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 […]

## This puzzle stumped a Math PhD student. But there is a clever way to solve it!

What is the height of the red bar? This puzzle was posted on Math StackExchange by a Math PhD candidate, so I did not feel bad when I was unable to solve it! (Though I suspect some people will even find it “easy.”) Math StackExchange (see solution by Eric Duminil). It was posted by a […]

## 2.920050977316 – Numberphile

Dr James Grime is discussing a new prime-generating constant. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ Extra footage from this interview: https://youtu.be/yXPhq-36Eq4 More James Grime videos: http://bit.ly/grimevideos James Grime’s website: https://www.singingbanana.com Mills’ Constant video: https://youtu.be/6ltrPVPEwfo A Prime-Representing Constant by Dylan Fridman, Juli […]

## A delightful logic puzzle from the Stanford Competitive Exam (1947)

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 […]

## How do brains count? – Numberphile

Professor Brian Butterworth is a neuroscientist who specialises in numbers and mathematics. More from this interview at https://youtu.be/FCS4b3OjVJM and earlier videos with him at: https://bit.ly/Brian_Butterworth More links & stuff in full description below ↓↓↓ Brian’s website: https://www.mathematicalbrain.com Brian Butterworth playlist: https://bit.ly/Brian_Butterworth Discussed papers… Auditory midbrain neurons that count: https://pubmed.ncbi.nlm.nih.gov/12219094/ Mapping human temporal and parietal neuronal […]

## 5 Circles Puzzle

Can you solve this neat geometry puzzle? Thanks to Joe M. for the suggestion! Sources https://brilliant.org/practice/circle-properties-level-2-3-challenges/?problem=day-5-five-golden-circles&subtopic=circles&chapter=circle-properties How I’m Learning to Step into Math Problems Circle puzzle 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. […]

## What Is The Area? A Clever “Outside The Box” Solution!

Can you solve this geometry gem? Special thanks this month to: Mike Robertson, Michael Anvari, Kyle. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Quora (many alternate solutions) https://www.quora.com/Inside-an-equilateral-triangle-there-is-a-point-which-is-5-6-and-7-units-away-from-the-3-vertices-respectively-What-is-this-triangles-area 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 […]

## The Forgotten Number System – Numberphile

Featuring author Alex Bellos – check his books (including the Language Lover’s Puzzle Book) on Amazon: https://amzn.to/3oU0wjT More links & stuff in full description below ↓↓↓ More Alex on Numberphile: http://bit.ly/Bellos_Playlist Alex’s own website with links to all his stuff: http://www.alexbellos.com Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also […]

## The Cat In The Hat Puzzle

Can you pass this logic test that stumps many people? References https://brilliant.org/problems/the-boxes/ http://www.dailymail.co.uk/femail/food/article-3905480/Are-smart-solve-beer-burger-brainteaser-Tricky-maths-puzzle-sweeping-web-harder-looks.html 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 […]

## Bomb Blast Radius – Numberphile

Featuring Tom Crawford. More links & stuff in full description below ↓↓↓ Tom Crawford website: https://tomrocksmaths.com/ More of our videos with Tom at: http://bit.ly/Crawford_Videos Atom bombs on Periodic Videos: https://youtu.be/QLZMzsRB86E Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging […]

## Spheres In A Cube Puzzle

What is the radius of each sphere? Reference http://puzzling.stackexchange.com/questions/41952/nine-identical-spheres-fit-exactly-into-a-cube 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 make videos. Be prepared–animation […]

## Solve if you are a “genius” – incredible hexagon puzzle!

Thanks to Elliott Line for the suggestion! Elliott is the editor of a bimonthly puzzle magazine, Enigma, available exclusively to members of Mensa (a high IQ society). Check out his website for many more great puzzles: http://www.elliottline.com/puzzles General solution method on Math StackExchange https://math.stackexchange.com/questions/2336865/area-of-a-hexagon-from-the-distances-of-the-opposite-sides Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I […]

## Belgian Mystery Number

Can you solve this problem asked to 14 and 15 year olds in the Belgian Mathematical Olympiad? 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 […]

## Colouring Knots – Numberphile

Featuring Professor Sylvain Cappell from NYU. Extra footage at: https://youtu.be/NV3EeagyU0Y More links & stuff in full description below ↓↓↓ Merch based on this video: https://teespring.com/numberphile-knots And here: https://teespring.com/numberphile-figure-eight Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with […]

## Square In A 3-4-5 Triangle Puzzle

What is the area of the square? Thanks to Papa in India for the suggestion! This puzzle is half of of problem 21 in the 2017 AMC 10A. https://artofproblemsolving.com/wiki/index.php/2017_AMC_10A_Problems/Problem_21 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 […]

## Interesting Angle Problem From Peru

Thanks to Juanci for the suggestion! Also thanks to everyone who shared a solution on Twitter. A special thanks to LuisAndrRomero2 who provided the first detailed solution. Special thanks this month to: Michael Anvari, Kyle. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Who can solve this one? I'm working on a video for it and […]

## Challenging Problem Given To 10 Year Old Students

This problem seems like it is impossible to solve because it does not have enough information. If the rectangle has an area of 10, what is the area of the triangle? 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 […]

## Hard Problem For 9 Year Olds In Taiwan

This problem went viral because even teachers had trouble solving it. It even got covered in television news! Can you figure it out? References BlackPenRedPen Twitter Find A, B, C, D, E. This was a 4th-grade math problem in Taiwan that made the news! I remember my friend gave this problem to me from her […]

## Impossible Viral Problem

What is the area of the triangle? References https://old.reddit.com/r/math/comments/51rr52/calculate_the_area_of_the_triangle_abc/ I agree with area=17.186554595799…My solution is at https://t.co/XjhoNYaKIZThanks for a great problem. Does anyone have an elegant solution? — Chris Harrow (@chris_harrow) September 22, 2018 Inscribed Triangle Challenge https://math.stackexchange.com/questions/1936580/how-to-relate-the-perpendicular-line-that-touches-a-circle-and-an-inscribed-tria https://foro.rinconmatematico.com/index.php?PHPSESSID=0dc1be1086008ebf0fec031f3a0ced1b&topic=96792.msg388692#msg388692 https://math.stackexchange.com/questions/1908861/using-trig-identity-to-solve-a-cubic-equation https://en.wikibooks.org/wiki/Trigonometry/The_solution_of_cubic_equations https://en.wikipedia.org/wiki/Law_of_sines Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all […]

## Poncelet’s Porism – Numberphile

Featuring Daniel Litt. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ Daniel Litt: https://www.daniellitt.com/ See Daniel previously on Numberphile: https://youtu.be/eYfpSAxGakI Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated […]

## Can You Solve This Logic Puzzle?

This is from a sample paper for the Online Mathematics Challenge 2020. Source THÁCH THỨC TOÁN HỌC TRỰC TUYẾN 2020 – Đề thi mẫu nhóm 9-10 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 […]