# Math

This logic test has 6 options and you need to find the correct answer. But each option refers to other options. So which one is correct? Source …

Thanks to Professor Peer Johannsen at Pforzheim University for creating this puzzle! Color four dots blue or erase four blue dots to make a valid equation: (10 + …

Check our sponsor The Great Courses Plus (free trial): http://ow.ly/j5cB30hIvm2 This video features Cliff Stoll. More links & stuff in full description below …

On the SAT exam, you have about 2 minutes to read and solve each math question. This one about averages can send you in a loop, unless you approach it …

Numberphile Playing Cards: http://bit.ly/NumberphileCards More card videos: http://bit.ly/Cards_Shuffling More links & stuff in full description below …

What is the radius of the circle, in simplest terms involving a, b, and c? I read that even the great mind Richard Feynman made a mistake. Watch the video to …

Thanks to Raoul from Indonesia! This problem stumped me, but I persisted and eventually figured it out. The key was thinking inside the box! My blog post for this …

I’m thinking of a three digit number where the number exactly equals the sum of the factorial of each digit. What is the number? My blog post for this video …

Truncatable Primes with Dr James Grime… Check out Brilliant (and get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links …

Thanks to Reio in Romania for emailing me this fun problem! What is the area? This puzzle was shared with the tagline “you should be able to solve this.

This is a (stand-alone) continuation of the previous video at: https://youtu.be/2vnqSwWAn34 Featuring Tadashi Tokieda. More links & stuff in full description …

Tadashi is back with a discussion of how we know where earthquakes occur. A second video is at: https://youtu.be/lubGnk0UZt0 More links & stuff in full …

Thanks to Tyler Cenko, and Caio Cerqueira from Brazil, for suggesting this wonderful number puzzle! I had a lot of fun solving this. Can you make 6 from 3 …

This delightful problem comes from a German math competition. What’s the perimeter of the triangle CDE? You have 3 minutes to solve this problem. Watch the …

A, B, and C share food at a party, and C pays A and B fairly. How much should each person get? The correct answer seems unfair, but it is surprisingly the only …

A cable of 80 meters (m) is hanging from the top of two poles that are both 50 m from the ground. What is the distance between the two poles, to one decimal …

A simple trick with some neat math behind it. More on Numberphile cards at: http://www.bradyharanblog.com/numberphile-playing-cards More links & stuff in full …

A 6 digit number abcdef has the following property. Make a table with 6 rows, where column i = 1, 2, 3, 4, 5, 6 is the number abcdef multiplied by i. (If the first row …

One of the most famous free kicks ever taken – but how far from the goal was Brazil’s Roberto Carlos? More links & stuff in full description below …

Thanks to Josh for this problem! And thanks to Folke for emailing it to me! There are 7 doors in a line. A mouse starts in the middle at door 4. At doors 1 and 7 are …

More Klein bottle videos: http://bit.ly/KleinBottles More links & stuff in full description below βββ Visit Cliff Stoll’s online store: http://www.kleinbottle.com/ More …

They say only geniuses can solve this puzzle, and this time they are correct. Thanks to all patrons! Special thanks to: Shrihari Puranik Kyle My blog post for this …

Check out Brilliant (and get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below βββ This video …

Thanks to Muztoba Ali in Bangladesh for this problem! Two brothers, A and B, have the exact same walking speed and the exact same running speed. One day …

Make the equation correct by adding one blue dot, or erasing one blue dot. A single dot changes everything! Sources …

In the game of Tetris, there are 7 pieces, each made up of 4 square units. (The shapes are called “tetrominoes” in mathematical literature.) Here’s the puzzle.

Tadashi discusses pressure and lift… with a toy of course! More links & stuff in full description below βββ Lift and wings on Sixty Symbols: …

People often send me puzzles they see on social media. They love these videos because learning how to solve them helps builds their confidence in math.

Which figures can you form from the two shapes A and B? This is a sample question from the 2017 NAEP for 8th grade US students. Be sure to select all of the …

Check out Brilliant (and get 20% off their premium service): https://brilliant.org/numberphile (sponsor)… More links & stuff in full description below βββ Check …

This inequality is famous in math competitions and in theoretical proofs. But why is it true? The video presents a great geometric visualization and proof for two …

Thanks to Oladele from Nigeria for suggesting this problem! Team A has 4 girls and 7 boys. Team A takes 5 days to paint 4 rooms. Team B has 7 girls and 10 …

Many people emailed me this apparent paradox showing 4 = 2. Can you figure out where the mistake is? My blog post for this video https://wp.me/p6aMk-80Q …

Thanks to Mike Painter for emailing me! This problem comes from a 1957 math class. A man is standing due East of a tower and notes it subtends an angle of 45 …

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 = ?

Check out Brilliant (and get 20% off) by clicking https://brilliant.org/numberphile (sponsor) Hannah Fry has a new book coming: https://amzn.to/2J6oCph (US) or …

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 …

Thanks to George who sent me this problem (created by 7th grade math teacher Ms. V)! There is a table in the video. The numbers in the first column are …

Discussing h-vectors and the g-conjecture. Featuring June Huh from the Institute for Advanced Study at Princeton University. More links & stuff in full description …

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, …

Signup for your free trial to The Great Courses Plus here: http://ow.ly/b5wA30hIviV (sponsor) More links & stuff in full description below βββ James Grime on a …

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 …

Limited edition “Golden Ratio” T-Shirts at Fibonacci prices: https://teespring.com/NP-Seeds and https://teespring.com/NP-Golden-Rectangle More links & stuff in …

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 …

Check out Brilliant (and get 20% off) by clicking https://brilliant.org/numberphile Featuring Ben Sparks — More links & stuff in full description below …

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