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### Mind Your Decisions

Shared publicly -This must be how the most interesting man in the world does math. "I don't always multiply numbers by hand, but when I do, I use this trick."

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This must be how the most interesting man in the world does math. "I don't always multiply numbers by hand, but when I do, I use this trick."

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interesting

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Math Problems from the movie Mean Girls

Blog Post

http://mindyourdecisions.com/blog/2015/08/02/mean-girls-math-questions-sunday-puzzle/#.Vb568PlVhBc

Video

https://www.youtube.com/watch?v=vtUnHqb_rfw

Blog Post

http://mindyourdecisions.com/blog/2015/08/02/mean-girls-math-questions-sunday-puzzle/#.Vb568PlVhBc

Video

https://www.youtube.com/watch?v=vtUnHqb_rfw

I started MindYourDecisions in 2007 and was amazed people cared about math and game theory, and this site even has been mentioned a few times in the press. I studied Economics and Mathematics at Stanford where I got straight A's. (almost). I love game theory and hope to read all the books on the ...

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Viral Exam Question, Killer Robots, And Greece- Game Theory News

http://mindyourdecisions.com/blog/2015/07/28/viral-exam-question-killer-robots-and-greece-game-theory-news/#.VbbtB_lVhBc

http://mindyourdecisions.com/blog/2015/07/28/viral-exam-question-killer-robots-and-greece-game-theory-news/#.VbbtB_lVhBc

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This Week In Math #3: Why cicadas are good at math, the red square puzzle, and understanding the monster group

http://mindyourdecisions.com/blog/2015/07/24/this-week-in-math-3-why-cicadas-are-good-at-math-the-red-square-puzzle-and-understanding-the-monster-group/#.VbKcXflVhBc

http://mindyourdecisions.com/blog/2015/07/24/this-week-in-math-3-why-cicadas-are-good-at-math-the-red-square-puzzle-and-understanding-the-monster-group/#.VbKcXflVhBc

I started MindYourDecisions in 2007 and was amazed people cared about math and game theory, and this site even has been mentioned a few times in the press. I studied Economics and Mathematics at Stanford where I got straight A's. (almost). I love game theory and hope to read all the books on the ...

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This PSAT Question Stumped Almost Everyone. Attaching A Tetrahedron To A Pyramid – Sunday Puzzle

A tetrahedron and a square pyramid have edges with the same length. The two shapes are attached on a triangular face with the vertices aligned to form a new shape. How many faces does the new shape have?

A) Five

B) Six

C) Seven

D) Eight

E) Nine

Blog: http://mindyourdecisions.com/blog/2015/07/19/this-psat-question-stumped-almost-everyone-attaching-a-tetrahedron-to-a-pyramid-sunday-puzzle/#.VawDdvlVhBc

Video: https://www.youtube.com/watch?v=rXIzUtLG2jE

A tetrahedron and a square pyramid have edges with the same length. The two shapes are attached on a triangular face with the vertices aligned to form a new shape. How many faces does the new shape have?

A) Five

B) Six

C) Seven

D) Eight

E) Nine

Blog: http://mindyourdecisions.com/blog/2015/07/19/this-psat-question-stumped-almost-everyone-attaching-a-tetrahedron-to-a-pyramid-sunday-puzzle/#.VawDdvlVhBc

Video: https://www.youtube.com/watch?v=rXIzUtLG2jE

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This is a Geogebra worksheet where you can play around with the shapes and see the result for yourself

http://tube.geogebra.org/student/m1442749

http://tube.geogebra.org/student/m1442749

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This Week in Math: US Team Wins the International Math Olympiad, An Elliptical Pool Table, And Solving The Die Hard Riddle With Mathematical Billiards

http://mindyourdecisions.com/blog/2015/07/17/this-week-in-math-us-team-wins-the-international-math-olympiad-an-elliptical-pool-table-and-solving-the-die-hard-riddle-with-mathematical-billiards/

http://mindyourdecisions.com/blog/2015/07/17/this-week-in-math-us-team-wins-the-international-math-olympiad-an-elliptical-pool-table-and-solving-the-die-hard-riddle-with-mathematical-billiards/

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Guessing Game With A Strategic Twist - Game Theory Tuesdays

I have randomly selected a whole number from 1 to 100. You have to figure out my number. After you make a guess, I will tell you if you are correct, or if my number is higher or lower. But each time you guess it costs you $1. How can you guess optimally and minimize your cost?

Game Theory Variation: What if I'm playing strategically? What will happen then? Solve the game if I'm choosing from the numbers 1, 2, 3.

http://mindyourdecisions.com/blog/2015/08/04/the-high-low-guessing-game-with-a-strategic-twist-game-theory-tuesdays/#.VcAe4flVhBc

I have randomly selected a whole number from 1 to 100. You have to figure out my number. After you make a guess, I will tell you if you are correct, or if my number is higher or lower. But each time you guess it costs you $1. How can you guess optimally and minimize your cost?

Game Theory Variation: What if I'm playing strategically? What will happen then? Solve the game if I'm choosing from the numbers 1, 2, 3.

http://mindyourdecisions.com/blog/2015/08/04/the-high-low-guessing-game-with-a-strategic-twist-game-theory-tuesdays/#.VcAe4flVhBc

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This Week In Math (#4): Obamacare Meme, Counter-intuitive PSAT Question, Lego Math

http://mindyourdecisions.com/blog/2015/07/31/this-week-in-math-4-obamacare-meme-counter-intuitive-psat-question-lego-math/#.Vbvo4PlVhBc

http://mindyourdecisions.com/blog/2015/07/31/this-week-in-math-4-obamacare-meme-counter-intuitive-psat-question-lego-math/#.Vbvo4PlVhBc

I started MindYourDecisions in 2007 and was amazed people cared about math and game theory, and this site even has been mentioned a few times in the press. I studied Economics and Mathematics at Stanford where I got straight A's. (almost). I love game theory and hope to read all the books on the ...

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You can tell if a number is divisible by 7 using this graph. But why does it work? Sunday Puzzle

Video

https://www.youtube.com/watch?v=vxHrfIom-YA

Blog Post (with proof)

http://mindyourdecisions.com/blog/2015/07/26/divisibility-by-7-test-using-a-graph-why-does-it-work-sunday-puzzle/#.VbV4SvlVhBc

Video

https://www.youtube.com/watch?v=vxHrfIom-YA

Blog Post (with proof)

http://mindyourdecisions.com/blog/2015/07/26/divisibility-by-7-test-using-a-graph-why-does-it-work-sunday-puzzle/#.VbV4SvlVhBc

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How Mandatory School Vaccinations Solve A Social Dilemma – Game Theory Tuesdays

http://mindyourdecisions.com/blog/2015/07/21/how-mandatory-school-vaccinations-solve-a-social-dilemma-game-theory-tuesdays/#.Va2n-_lVhBc

http://mindyourdecisions.com/blog/2015/07/21/how-mandatory-school-vaccinations-solve-a-social-dilemma-game-theory-tuesdays/#.Va2n-_lVhBc

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An Awesomely Evil Test Question And The Correct Game Theory Answer

Blog post with detailed discussion

http://mindyourdecisions.com/blog/2015/07/14/an-awesomely-evil-test-question-and-its-mathematical-answer-game-theory-tuesdays/#.VaR86PlVhBc

Video with summary

https://www.youtube.com/watch?v=j9PXeNcoagw

Blog post with detailed discussion

http://mindyourdecisions.com/blog/2015/07/14/an-awesomely-evil-test-question-and-its-mathematical-answer-game-theory-tuesdays/#.VaR86PlVhBc

Video with summary

https://www.youtube.com/watch?v=j9PXeNcoagw

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A Fun Statistics Problem About Standard Deviation – Sunday Puzzle

1. Solve for Y so that the set {1, 2, 3, Y} has the same standard deviation of {1, 2, 3}.

2. Solve for Y so that the set {1, 2, 3, …, N, Y} has the same standard deviation of the set of consecutive numbers {1, 2, 3, …, N}.

Answer:

http://mindyourdecisions.com/blog/2015/07/12/a-fun-statistics-problem-about-standard-deviation-sunday-puzzle/#.VaLOtflVhBc

1. Solve for Y so that the set {1, 2, 3, Y} has the same standard deviation of {1, 2, 3}.

2. Solve for Y so that the set {1, 2, 3, …, N, Y} has the same standard deviation of the set of consecutive numbers {1, 2, 3, …, N}.

Answer:

http://mindyourdecisions.com/blog/2015/07/12/a-fun-statistics-problem-about-standard-deviation-sunday-puzzle/#.VaLOtflVhBc

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