# Math

Did you know Google can help with math calculations? These are 5 of my favorite tricks you have to try. 6÷2(1+2) …

Here’s the video everyone requested after the average distance in a square video. What’s the average distance of two points on a circle? Can you figure it out?

Stanford is one of the top universities in the world. Can you solve these historical entrance exam problems from 1892? And thanks to Erik for finding a typo in the …

Lacking proper equipment, two friends devise a way to measure how long the train is based on their walking steps. Can you solve for the length of the train?

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

This is a convincing geometric argument and you have to really know your math to figure out where the mistake is. Thanks to Eszter from Hungary for suggesting …

Thanks to Devan from Lilin Bangsa Intercultural School for suggesting this problem! What is the radius of the small circle in between the blue circle (radius 4) …

Peter Winkler’s excellent book “Mathematical Puzzles: A Connoisseur’s Collection” states this easy problem is known to frustrate even great mathematicians.

Thanks to Ohad from Israel for suggesting this problem! A square with side length 5 has its corner at the center of a square with side length 4. The two squares …

This simple problem for kids is sure to stump some adults. Can you figure out the height of the table? Problem adapted from …

Thanks to Mika from Sweden for suggesting this problem! Most of the games end in a draw, but some will be wins for you, and others will be wins for your skilled …

What is 60÷5(7-5) = ? Everyone is arguing about this problem, so let’s figure out the correct answer! The problem involves the order of operations, historical math …

A calculus problem went viral! Some major websites are reporting that students at a university in China had to solve this for the WiFi password in a dining hall.

Featuring Professor Elisabeth Werner. Part 2 is on our Numberphile2 channel: https://youtu.be/HXqzs5Q0G0A More links & stuff in full description below …

I wish I knew this trick while I was in school. Can you solve for the red area? Source …

What value is each letter? This is an incredible math problem with just a single solution! Can you figure it out? My blog post for this video …

Seriously? Matt Parker is talking about Fibonacci and Lucas numbers again. Part 2: https://youtu.be/z1THaBtc5RE More links & stuff in full description below …

Thanks to Yale from Hong Kong for suggesting this problem! This problem went viral after Carl Ho’s video (in Chinese), and there are many fun ways to solve it.

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

Thanks to Peter for sending me this problem! This is a really fun one and I encourage you to work it out. A priest and a cantor have a conversation about the …

Thanks Audible for sponsoring this video. Start a 30-day trial & receive a free audiobook at https://www.audible.com/numberphile or text numberphile to 500 500 …

These are some fun problems you can share at a party or in a bar/restaurant. Can you figure them out? This Matchstick Puzzle Is “Extremely Hard” For Adults …

Thanks to Omer from Israel for suggesting this type of puzzle! Three friends rotate playing 1-on-1 basketball games. If A played 8 games, B played 11 games, …

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

Thanks to Eric from Miami for suggesting this problem and sending a solution! The diagram shows a quadrilateral ABCD with the values for some angles and the …

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 …

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