## Sunday, March 29, 2015

### Math Teachers at Play 84

Welcome to the 84th Math Teachers at Play Blog Carnival!

84 is a portentous number. It's the sum of twin primes (What's the previous sum of twin primes? Next?). It's thrice perfect, twice everything.  It's positively Orwellian. It's even a town in Pennsylvania. It's a game (actually a variant of the domino game 42 if you play with 2 sets.) It is the #edtech that shall not be named.

 (click for full size image)
84 puzzler 1:
Number the intersections of these five circles with the integers 1 to 20 so that the points on each circle sum to the same.

An exciting development this week was Jed Butler unveiling the Math Twitter Blog-o-Sphere Directory. It will be a great resource, but only if you add your information! Maybe you blog, maybe you tweet, maybe not... but you are a mathy type on the interwebs or you wouldn't be reading this!

It was a good month for math reading related posts.

84 Puzzler 2
84 is a side length in the smallest integer perfect tetrahedron, and is tetrahedral number to boot. Which triangular pyramid has 84 points? How many points in the nth pyramid?

Tool Tips

Attributed

84 Puzzler 3
What is the odd pattern that produces these multiples of 84? Highlight for hint: 7 is involved.
0, 2184, 78120, 823526, 4782960, ...

Why Do We Do the Things We Do?

Lesson Lab

That concludes the carnival; 84 cheers! Remember, you can submit posts to the next carnival via Denise's MTaP form. If you didn't see last month's Carnival 83, it was at CavMaths. We're looking for a host for Carnival 85 - can we come over to play at your blog? Email the Founder of This Here Shindig to give the all clear. Thanks to everyone who pitched in with submissions!

Number fact references: Archimedes Lab, MathWorld and Wikipedia.

GeoGebra sketch of the tetrahedral numbers.