In today's post, I've gathered a few free goodies for you!

They're all about mental math, so you may wind up learning something if you go through all of them!

• 2011 “Lightning Calculation” Calendar: Yes, August 2012 is probably a strange time to be recommending a 2011 calendar, but this calendar still has a valid purpose. Each month teaches new mental math techniques, and the calendar itself then gives you related daily challenges to practice! Naturally, there are calendar calculations, but there's multiplication, squaring, trigonometry and more. If you like this calendar, you might want to explore the rest of the author's site, as well.

• Short-Cut Math: This is a clearly-written guide to the mental math shortcuts you're most likely to need during your lifetime. Various publishers still market this book, but the original at the link is still public domain. The section on the under-utilized technique of casting out 9s always makes me think of this amusing anecdote, in which an adult learns the technique for the first time, and it actually provokes a violent reaction!

Ars Calcula: This is a simple blog about mental math, and each entry teaches one specific mental math technique. It's not much else than that, but it neither claims nor needs to be any more. The multiplication guide is especially handy, as it gives a sort of hierarchy of when each multiplication technique is appropriate.

Vedic Mathematics: My Trip to India to Uncover the Truth (Alex Bellos): Back in 2011, Gresham College hosted a series of lectures about early mathematics in various cultures. In my opinion, Alex Bellos had the most intriguing lecture of the group, in the video below. Vedic Mathematics is said to be an ancient approach to mathematics, but Alex Bellos questions that history, and then even questions whether the answer is important or not. His powerpoint slides, a transcript, and both audio and video of this presentation are available for download at the link (scroll down to Crore blimey! My trip to India to Uncover the Truth about Vedic Mathematics).



Arthur Benjamin at Etech: You've more than likely seen Arthur Benjamin's Mathemagic performance at TED, but that video only gives a taste of his complete show. This paragraph's main link, however, is a more complete, 37-minute-long version of his show at Etech. There are many aspects you wouldn't expect, such as opening with a card trick, and even teaching the audience some mental math they can use!



Everything above is free and legal to download if you wish to save it to your hard drive. This may not seem like much, but if you take the time to really explore each item, you'll have enough food for thought for quite some time!