## Two new videos by James Tanton

After a hiatus of several months Dr. Tanton is making videos again. Here are two new ones.

Lulu has two children. You are told that at least one of her children is a boy who was born on a Tuesday. What is the probability that her other child is also a boy?

The answer will surprise you!

Here is a cute geometry puzzle: Imagine you are an archeologist and have come across just a small section of a rim of an ancient wheel. What size wheel did it come from?

This is a great puzzle to give to geometry students too. Hand out a picture of an arc of a circle and ask if is possible to find the measure of that arc using only basic tools - and them have students actually do it.

## An infinite number of mathematicians walk into a bar …

From Instapundit

Math joke from Anna, the bartender and civil engineering student: an infinite number of mathematicians walk into a bar. The first one tells the bartender he wants a beer. The second one says he wants half a beer. The third one says he wants a fourth of a beer. The bartender puts two beers on the bar and says “You guys need to learn your limits.”

Hat tip to Algut Runeman at MathFuture.

## Paper-folding proof of Pythagoras

Here's a great video by Vi Hart that shows a couple of proofs of the Pythagorean Theorem. Nothing new in terms of the proofs; they're ones I've seen often. What's clever about Vi's approach is that she uses paper-folding to create the elements of the proof. I like this kinesthetic approach to a couple of familiar proofs.

As always with Vi's exuberant videos, it would be nice to be able to watch them at half speed!

Enjoy!

## Review: Number-Crunching: Taming Unruly Computational Problems from Mathematical Physics to Science Fiction

Great stories. Interesting and challenging problems. Instructive MATLAB code. Lots of physics. That's my in-a-nutshell assessment of Princeton University Press's hot-off-the-press Number-Crunching: Taming Unruly Computational Problems from Mathematical Physics to Science Fiction.

Paul Nahin is a great story teller. Some of you might recall my review of an earlier book of Nahin's An Imaginary Tale where I noted Nahin's enjoyable writing style. Nahin has, in fact, written quite a number of books.

Nahin takes on the subject of using computers to solve difficult problems, many in physics, that couldn't be solved before computers. The publisher's page introduces some of the problems.

How do technicians repair broken communications cables at the bottom of the ocean without actually seeing them? What's the likelihood of plucking a needle out of a haystack the size of the Earth? And is it possible to use computers to create a universal library of everything ever written or every photo ever taken? These are just some of the intriguing questions that best-selling popular math writer Paul Nahin tackles in Number-Crunching. Through brilliant math ideas and entertaining stories, Nahin demonstrates how odd and unusual math problems can be solved by bringing together basic physics ideas and today's powerful computers. Some of the outcomes discussed are so counterintuitive they will leave readers astonished.

## Review: The Man of Numbers: Fibonacci’s Arithmetic Revolution

Keith Devlin is a prolific writer. As The Math Guy on National Public Radio and author of some 40 books, Keith Devlin makes a tremendous contribution toward making math more accessible to the public.

The Man of Numbers: Fibonacci's Arithmetic Revolution is Devlin's latest book.

"The Man of Numbers," at 156 pages (plus notes, bibliography, and index) and ten chapters is a fairly quick read. Leonardo of Pisa, also known as Fibonacci, is mostly only known for the Fibonacci sequence. Devlin shows us that there was much more to Fibonacci's life and that, in fact, Fibonacci played a very key role in the marketing of arithmetic in 1202 to the world of commerce in Western Europe through his book, Liber Abacci (The book of calculation.)

I'm not going to review the book chapter by chapter as you can find that kind of information on the web. NPR has a nice review, an excerpt from the book, and an audio interview with Mr. Devlin. ScienceNews.org has a review and Amazon.com has several reviews. But, I will point out some items of particular interest.

## 81st Carnival of Mathematics

Welcome to the September 2, 2011 edition of carnival of mathematics.

This is the 81st edition. In the tradition of the Carnival of Mathematics, we provide trivia on the number of the edition.

- 81 is 3^4 and also 9^2.
- The awesome card get, Set, contains 81 cards.
- 81 is the square of the sum of its digits. Thanks to this site.
- 81 is a heptagonal number and a 28-gonal number.
- There are 81 stable chemical elements.

Some more trivia about the number 81 appears here.

That concludes this month's Carnival of Mathematics. Oops, we've not mentioned our submissions. There are lots this month. Here they are ...

**Mike Croucher**, owner of the Carnival of Mathematics, presents A retrospective of 4 years of mathematical articles at WalkingRandomly. Happy Birthday, WalkingRandomly! I'm a big fan of Mike's blog and I discovered a bunch of neat articles among his most popular.

**Mike Croucher** also nominated these two articles:

## Martin Cohen on a variety of exceedingly elementary proofs

Martin Cohen is blogless yet he wants to share his paper, Exceedingly Elementary Proofs That a^(1/n) -> 1, n^(1/n) -> 1, and (1+1/n)^n -> e. I offered a home for the paper. I created a PDF and have placed it here.

Martin would love your feedback on the paper. Please leave comments here or contact him at the email address in the paper.