The Cooperative Bank of Kenya, one of Kenya's largest banks, tweeted out this problem. If 4 + 2 = 26, 8 + 1 = 79, 6 + 5 = 111, then what is 7 + 3 = ? My challenge: if 7 + 3 = z, solve for another pair of numbers x + y = z. Very few can solve this challen...

From MindYourDecisions

Hippocrates of Chios solved this, nearly 100 years before Euclid even wrote The Elements, and before we knew the exact formula for the area of a circle. This is said to be the first precise mathematical of the area between two curved lines. Learn how he s...

From MindYourDecisions

Thanks to Brian Galebach who created and sent me this problem! You arrive at a park where geysers A, B, and C erupt at intervals of precisely 2, 4, and 6 hours, respectively. Each started erupting independently at a random time in history, unknown to you....

From MindYourDecisions

Another day, another viral math problem! Lighthouses A, B, and C turn on and off in regular intervals. A shines light for 3 seconds, then is off for 3 seconds, and repeats this cycle. B cycles 4 seconds on/4 seconds off, and C cycles 5 seconds on/5 second...

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Thanks to Tim for sending this problem! The total amount of sand contained in Boxes A, B and C is 360 grams. First a mathematician pours 1/6 of the sand from Box A into Box B. After that, the mathematician pours 1/3 of the sand in Box B into Box C. Finall...

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Some Scottish students felt the National 5 Maths Exam was too difficult, particularly this tricky umbrella question. The test is not yet released, so I have re-constructed the problem as best as I could from accounts of the exam. Here is the problem: "Can...

From MindYourDecisions

Thank you for 100 million views! To celebrate, here's a puzzle related to 100 million, sent by Karin. Find a sequence of 100 million consecutive non-prime numbers. That is, every number is composite—not a single number is a prime number. The method can ...

From MindYourDecisions

Mathematician Ed Southall, from the University of Huddersfield, created a stir when he tweeted this problem (@solvemymaths). The problem was covered in "The Daily Mail" and "The Sun." In this video I present one way to solve it.
My blog post for this vid...

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Thanks to Kshitij from India for sending me this problem! "A leaf is torn from a paperback novel. The sum of the numbers on the remaining pages is 15000. What are the page numbers on the torn leaf?" Notes: a leaf is a single sheet of paper, and the book i...

From MindYourDecisions

Problematic Men is a Korean TV show that featured puzzles solved by contestants, many of whom had genius IQ levels over 150. One of the puzzles was: if 9981 + 1601 = 2957, then 1080 + 9168 = ? It was remarkably solved in less than a minute by one contesta...

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This problem caught the attention of Bollywood celebs, including Sonam Kapoor, Aditi Rao Hydari, and Diana Penty, after fashion magazine editor Jitesh Pillai tweeted it. How many triangles are there? This is not just a simple test of observational ability...

From MindYourDecisions

This problem is tricky even for people who are good with numbers. Can you make 24 from the numbers 3, 3, 8, 8? You can use the operations + - × ÷ ( ). You have to use all four numbers (the digit 3 two times and the digit 8 two times). There are no tric...

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"One day it started snowing in the morning at a heavy and steady rate. A snowplow started out at noon, going 2 miles in the first hour and 1 mile in the second hour. What time did it start snowing?" Say what?! This is a famous problem from the 1942 book "...

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You're going to tell me 1 dollar equals 100 cents. But mathematically, 1 dollar is really equal to 1 cent. Don't believe me? Watch the video for a proof that will blow your mind.
In 2006, several Verizon support representatives actually said $0.002 equal...

From MindYourDecisions

Thanks to Hyeong-jun (H. J.) for emailing me this problem! This is a challenging problem from the math section of the 1997 CSAT, a standardized test in South Korea. Can you figure it out? It took me several attempts, but it was really satisfying when I so...

From MindYourDecisions

Lady Karren Brady tweeted this puzzle with a challenge to solve in 3 minutes, and it stumped Piers Morgan, who obviously need to watch MindYourDecisions to learn the order of operations ;) Can you figure it out?
My blog post for this video
https://wp.me/...

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Thanks to Daniel from Hungary for sending me this question from a math exam! When empty, a container fills completely from a faucet in A hours. When full, the same container drains completely if its drain is open for B hours. If the faucet is on and the d...

From MindYourDecisions

What is the sum of a geometric series for a finite number of terms? What about an infinite number of terms? The video presents an animated proof of the famous formulas. Once you understand it, you can test yourself by solving the problem: what is 6 + 66 +...

From MindYourDecisions

In a world where simple math problems spark huge debates online...YOU are the last hope to save mathematics.
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...

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Thanks to Lucas from Brazil who sent this problem! This is a proof that 3 = 0 using sneaky algebra that I had never seen before (this is a sneaky mistake, not a simple divide by 0 fallacy). Every step seems correct, but the conclusion is clearly false. Ca...

From MindYourDecisions

Thanks to James M. for this suggestion! You roll a dice up to 3 times, stopping after any roll you wish. You get paid the value of the roll you stop. If you play optimally, what is your expected payout? (more precise wording in video)
My blog post for th...

From MindYourDecisions

I saw this on the Saint Louis Science Center Twitter account and I admit, I was not able to figure it out! Can you?
My blog post for this video
https://wp.me/p6aMk-7Uw
Source
https://twitter.com/STLScienceCtr/status/823734248532217857
If you like my vi...

From MindYourDecisions

Thanks to Alessio from Italy for creating this problem and sending it to me! A cyclist and a series of motorcycles are racing to the top of a long climb, and the cyclist doubles back. Given how many motorcycles passed the cyclist, can you figure out the m...

From MindYourDecisions

This question has generated a lot of debate online. BuzzFeed's video has 450,000+ views already. But the question has a mathematical interpretation with a correct answer: in topology, how many holes does a straw have? I explain and animate the answer in t...

From MindYourDecisions

It's not the famous Cheryl's birthday problem...According to Mothership, this math problem is causing a lot of confusion: "There are 37 students in a class. How many students, at the least, are born in the same month?" Now I think the problem intended for...

From MindYourDecisions

Here's a mysterious puzzle you could share with a special person. If ∑8dh = loan, and ∓8rΠ = torii, then what is 128√e980 = ?
I usually mention sources. The 128√e980 is a meme whose origin I cannot trace. The other parts of the puzzle I devised....

From MindYourDecisions

Little known fact: Abraham Lincoln was a very good math student! In this video I share the story of why he studied Euclid's Elements. I also share a problem he did while in school. He did in fact get the correct answer, and we can deduce the steps he took...

From MindYourDecisions

Media outlets around the world are reporting on these math problems that have "flummoxed" everyone. As these got so much attention, I wanted to share some of the headlines and give a small discussion about what I think is the real lesson of these problems...

From MindYourDecisions

Did you know some math problems were used to discriminate against groups of people? This is one such problem, and it stumped me! But it has an unbelievably elegant solution. Take any equilateral triangle and pick a random point inside the triangle. Draw ...

From MindYourDecisions

On January 22, 2018, Facebook Open Source tweeted to announce the "flick," a unit of time to help sync various video frame rates and audio sampling frequencies. The media loved the story and some explained the idea. But no one explained where the mysterio...

From MindYourDecisions

Thanks to Halvor Kjærås for creating this logic puzzle! Barney says he caught 5 fish, and Alfred says he caught 2. But each person fibs about numbers when spoken aloud. Can you figure out how many each person actually caught?
My blog post for this vide...

From MindYourDecisions

Thanks to Kristian from Norway for sending me this problem! A three digit number is re-written with multiplication symbols between the digits, and the product is equal to one-fifth the original number. What was the original three digit number? Watch the v...

From MindYourDecisions

The Online Math Olympiad is a contest for high school students with challenging problem. This 2016 test had an average score of 9 out of 30. This video is an adaption of problem 16 which is an interesting probability puzzle. At the end of day 0, six magic...

From MindYourDecisions

The number N = 69,720,375,229,712,477,164,533,808,935,312,303,556,800 is special - it is the smallest number that has all numbers 1 to 100 as factors. The puzzle: what is the prime factorization of N? Watch the video for a solution. Thanks to Chunie for ...

From MindYourDecisions

Follow the simple instructions in the video and the result will be a fun mathematical effect! The trick got really popular a couple of years ago, but no one explained exactly why it worked. So in this video I also give the reason why the effect works out....

From MindYourDecisions

This is a fun little geometry problem inspired by a suggestion from Yossi Rozhenko. If the red area equals the blue area, what is the value of: (large circle's radius)/(small circle's radius)?
Small correction: At 3:07 I should have said "4 minus pi."
M...

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Luuk stumped his math teacher with one of my puzzles. Then his math teacher gave him a problem that Luuk suggested to me. If AAA + BBB + CCC = BAAC, what is the value of each digit? The digits are distinct and whole numbers from 1 to 9. Watch the video fo...

From MindYourDecisions

A convex quadrilateral is divided into four parts by its diagonals. Three of the areas are 2, 1, and 3 as shown in the diagram. What is the area of the fourth region?
Thanks to Gerrit for sending me this geometry problem and a solution! You guys have rea...

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